An apple’s color is set by pigments in its skin, mostly green, yellow, and red ones mixed in different amounts. Whether an apple can turn red at all is largely written into its genes, a switch that is on in red varieties and off in green and yellow ones. The weather and the tree add a second layer, so two apples of the same variety can look quite different.
The Three Pigments Behind Every Apple Color
Apple skin holds chlorophyll (the green pigment), carotenoids (the yellow pigment), and anthocyanins (the red pigment). These are the same pigment families found in leaves and flowers.1PubMed Central. Study on the differences of gene expression between pear and apple wild cultivation materials based on RNA-seq technique The skin color you see is a blend of how much of each is present.2Critical Reviews in Plant Sciences. Regulation of skin color in apples
Blending explains the in-between colors. A green-gold apple still has some green pigment hiding its yellow. A red apple over a yellow background shows both pigments at once, and the orange-red tones you see on some apples come from red layered over yellow.
Green has to fade before yellow can show. Green pigment is the strongest color factor in a yellow apple like Golden Delicious.3Journal of the American Society for Horticultural Science. Color Development in ‘Golden Delicious’ Apples Yellow only becomes visible once the green drops very low, even when yellow pigment is already there.4Journal of the American Society for Horticultural Science. Color Development in ‘Golden Delicious’ Apples So a Golden Delicious picked early looks green and turns yellow as its green pigment breaks down during ripening.5Horticulturae. MdSGR2 Negatively Regulates Chlorophyll Degradation in Apple That yellowing keeps going after harvest, driven by the apple’s own enzymes.6Journal of the American Society for Horticultural Science. Temperature Affects Postharvest Color Change of Apples Granny Smith, by contrast, keeps its green pigment as it ripens, which is why it stays green.7Horticulturae. MdSGR2 Negatively Regulates Chlorophyll Degradation in Apple Picking time changes how fruit looks in the bowl: an early-picked yellow variety may still look greenish, while a fully tree-ripened one looks clearly golden. In the produce aisle, a red apple with a yellow-green patch at the stem or bottom is showing its background color, and that patch is one ripeness hint, often more useful than the red.
Genes Decide Whether an Apple Can Turn Red
Red in apples is turned on by a control gene that starts the whole chain of red-pigment making.8PubMed Central. Red colouration in apple fruit is due to the activity of the MYB transcription factor, MdMYB10 Deep-red varieties like Jonathan run this switch much harder than pale-red ones.9PubMed. Isolation and functional analysis of a MYB transcription factor gene that is a key regulator for the development of red coloration in apple skin The switch itself is the same in red and paler apples; what differs is how strongly it is used.10PubMed Central. Red colouration in apple fruit is due to the activity of the MYB transcription factor, MdMYB10 Green and yellow apples still make related colorless compounds, but they lack the final steps that lead to red.11Critical Reviews in Plant Sciences. Regulation of skin color in apples
That is why a green apple won’t redden on a sunny windowsill. Without the active red gene, light has nothing to switch on. Granny Smith stays green no matter how much sun it gets.
Red varieties need both the gene and the right conditions. In them, the gene sets the ceiling and the weather decides how close an individual apple gets to it.
Breeders can now read the gene directly. This one gene region explains about half of the differences in how red apples are.12Euphytica. Allelic composition of MdMYB1 drives red skin color intensity in apple (Malus × domestica Borkh.) and its application to breeding An apple with two copies of the red version is redder than one with a single copy.13Euphytica. Allelic composition of MdMYB1 drives red skin color intensity in apple (Malus × domestica Borkh.) and its application to breeding Because the region can be read from a tiny leaf sample, breeders can test tiny seedlings and predict red skin about 9 times out of 10, years before fruit appears.14PubMed. A and MdMYB1 allele-specific markers controlling apple (Malus x domestica Borkh.) skin color and suitability for marker-assisted selection The prediction is strong but not perfect, since other genes and growing conditions also shape the final color.
Sun and Cool Nights Make Red Apples Redder
Ultraviolet light switches on the red-color gene in apple skin.15PubMed. Isolation and functional analysis of a MYB transcription factor gene that is a key regulator for the development of red coloration in apple skin UV combined with ordinary sunlight boosts red far more than either alone.16Physiologia Plantarum. Relative effectiveness and interaction of ultraviolet‐B, red and blue light in anthocyanin synthesis of apple fruit Apples grown under low UV ripen later, stay smaller, and carry less red pigment.17PubMed. Solar UV light regulates flavonoid metabolism in apple (Malus x domestica) So the sun-facing cheek of an apple is often redder than the side against a leaf.
That leaf can leave a record. A pale or green patch shaped like a leaf shows where it sat against the fruit and blocked light while the rest of the skin colored up.
Position in the tree matters too. The best-colored fruit hang high in the tree where they get the most light.18Horticulturae. Fruit Position, Light Exposure and Fruit Surface Temperature Affect Colour Expression in a Dark-Red Apple Cultivar Some growers lay shiny film on the orchard floor to bounce light up into the lower branches, and those apples develop more red blush over more of their surface.19HortTechnology. The Effects of Reflective Film on Fruit Color, Quality, Canopy Light Distribution, and Profitability of ‘Mondial Gala’ Apples
Cool nights help as well. Cold also switches on the red-color gene.20PubMed. Isolation and functional analysis of a MYB transcription factor gene that is a key regulator for the development of red coloration in apple skin Apples ripening during warm nights come out less red than those with cool nights.21Scientia Horticulturae. Night-temperature effects on rate of apple fruit maturation and fruit quality A hot autumn can therefore leave a normally red variety looking pale or streaky.
If you have a backyard tree, pruning to open up the canopy lets more light reach the fruit, and it is the most dependable way to improve color. The same variety grown in a warm region with hot nights may color less well than one grown further north, so choose varieties suited to your area.
Why Some Apples Are Striped and Others Solid Red
Varieties like Honeycrisp and Fuji can produce both striped and fully blushed forms.22PubMed Central. Skin Color in Apple Fruit (Malus × domestica): Genetic and Epigenetic Insights In the green stripes, the red gene’s start region carries extra chemical tags that turn it down.23PubMed Central. Skin Color in Apple Fruit (Malus × domestica): Genetic and Epigenetic Insights A solid-red Fuji form, Beni Shogun, has fewer tags on that gene and more red pigment than striped Fuji.24Scientia Horticulturae. Differential gene expression and epigenetic analyses between striped and blushed skinned sports of ‘Fuji’ apple When these tags change, a branch can suddenly start bearing differently colored fruit.25Horticulture Research. Multi-omics analyses reveal MdMYB10 hypermethylation being responsible for a bud sport of apple fruit color
A grower notices one branch bearing redder fruit, cuts a twig from it, and grafts it onto other trees, producing more trees with the new color. Many of the apples you buy come from redder branches of older varieties found this way, and their flavor usually stays close to the original. At the store, a striped apple shows narrow red streaks over a yellow or green base, while a blushed one is red across a broad area.
Why Some Apples Are Red Inside
Red flesh in some apples comes from a second control gene, a copy of the skin-red gene that arose long ago.26PubMed Central. An Ancient Duplication of Apple MYB Transcription Factors Is Responsible for Novel Red Fruit-Flesh Phenotypes It can make the flesh red without making the skin red.27PubMed. Expression and functional analysis of a novel MYB gene, MdMYB110a_JP, responsible for red flesh, not skin color in apple fruit In other red-fleshed apples, the usual red gene is pushed harder by a helper gene, and how hard it is pushed sets how deep the flesh color goes.28PubMed Central. A Functional InDel in the WRKY10 Promoter Controls the Degree of Flesh Red Pigmentation in Apple
Cut one open and you may find anything from faint pink streaks near the skin or core to deep red all the way through. The skin is not a reliable guide: some have red skin and red flesh, while others have a plain skin and a surprise inside. The red is the same kind of pigment as in red skin, so it is a natural color, not a dye. Many red-fleshed apples are newer varieties, so you are more likely to find them at farmers’ markets or specialty sellers than in a standard grocery aisle.
Does Color Tell You Taste or Nutrition
People tend to expect a redder apple to taste sweeter.29Konica Minolta Sensing. How Color Affects Your Perception of Food But Red Delicious was bred for looks and tough, bruise-resistant skin more than flavor.30The Counter. The Red Delicious is an apple atrocity. Why are we growing billions of pounds of them each year?
Sun does make a difference, though. Apples from the outer, sunlit part of the tree are generally sweeter, less sour, and higher in antioxidants than shaded inner fruit.31HortScience. Apple Compositional and Peel Color Differences Resulting from Canopy Microclimate Affect Consumer Preference for Eating Quality and Appearance Peels of red varieties like Starkrimson had the highest antioxidant levels, while Golden Delicious and Granny Smith had the lowest.32Scientia Horticulturae. Peel and flesh antioxidant content and harvest quality characteristics of seven apple cultivars Still, variety matters more than any one feature, and even within a variety some strains have fewer of these compounds.33PubMed. Phenolic composition and free radical scavenging activity of different apple varieties in relation to the cultivar, tissue type and storage Eating the peel gives you most of these compounds, whatever the color.
To pick sensibly, compare apples of the same variety. The better-colored one usually got more sun and tends to be a little sweeter, while comparing a red variety to a green one only tells you about genes. A background color shifting from green toward yellow suggests the apple is riper. Smell and firmness tell you more about eating quality than redness alone, so a firm, fragrant apple is a better bet.
Brown Patches and Browning After Cutting
Cutting, peeling, or bruising breaks apple cells open.34European Food Research and Technology. Trends in biochemical, anatomical mechanisms and molecular aspects in enzymatic browning of apples: a review An enzyme inside then meets the apple’s natural compounds and oxygen and makes a brown pigment.35PubMed. Chemical inhibition of polyphenol oxidase and cut surface browning of fresh-cut apples Lemon juice or an airtight container slows browning by limiting that reaction.
Some apples have a rough, dull brown skin.36PubMed Central. Russeting in Apple is Initiated after Exposure to Moisture Ends: Molecular and Biochemical Evidence It starts when moisture on young, fast-growing fruit makes the waxy skin develop tiny cracks.37PubMed Central. Russeting in Apple is Initiated after Exposure to Moisture Ends: Molecular and Biochemical Evidence Once it dries, the apple grows a corky layer under the cracks, like bark, which becomes the brown surface.38PubMed Central. Russeting in Apple is Initiated after Exposure to Moisture Ends: Molecular and Biochemical Evidence Scrapes and wounds produce the same corky layer.39PubMed Central. Apple fruit periderms (russeting) induced by wounding or by moisture have the same histologies, chemistries and gene expressions
Rough brown skin is a texture, not rot or mold, and some varieties are russeted by nature and prized for flavor. Brown cut flesh is safe to eat, just less appealing, because the browning comes from the enzyme reaction with air, not spoilage. A soft, wet brown spot is a different matter, since it suggests bruising or decay and is worth cutting away.
Stored apples are kept cold and low in oxygen, which slows the green-to-yellow change so they look fresh for months. Some storage operations also treat apples with a ripening blocker that slows color change.40HortScience. Impacts of 1-Methylcyclopropene and Controlled Atmosphere Established during Conditioning on Development of Bitter Pit in ‘Honeycrisp’ Apples