Color blindness is diagnosed through a series of visual tests that measure how accurately you distinguish between colors. The most common starting point is a screening test using colored dot plates, which takes under five minutes and catches roughly 97% of red-green deficiencies. From there, more specialized tests can pinpoint the exact type and severity of your color vision deficiency.
The Ishihara Plate Test
The test you’re most likely to encounter is the Ishihara color plate test, used in eye clinics, pediatrician offices, and school screenings worldwide. You’ll look at a series of circular plates filled with colored dots of varying sizes. Hidden within each pattern is a number or shape that people with normal color vision can easily spot but that partially or fully disappears for someone with a color vision deficiency.
The concise edition uses 14 red-green test plates plus one demonstration plate. The current passing threshold is 12 correct out of 14. Scoring below 12 indicates a color vision deficiency, and this cutoff has been shown to catch deficiencies with 97% sensitivity and 100% specificity, meaning it rarely misses a real case and almost never flags someone who sees color normally.
The Ishihara test is excellent for detecting red-green color blindness, which accounts for the vast majority of inherited cases. It does have a significant limitation: it cannot detect blue-yellow deficiencies. For that reason, clinicians sometimes use the Hardy-Rand-Rittler (HRR) plate test instead. In a study comparing the two for detecting color vision loss caused by optic nerve disease, the HRR test correctly identified 79% of affected patients while the Ishihara caught only 48%, both with perfect specificity. The HRR plates include patterns designed to reveal blue-yellow confusion, making them a better choice when acquired color vision loss is suspected.
Color Arrangement Tests
If a screening test flags a deficiency, a more detailed assessment often follows. The Farnsworth-Munsell 100-Hue test is the most widely used arrangement test. Instead of reading numbers from dotted plates, you sort colored caps into order. The test contains 85 color samples divided into four boxes, each representing a segment of the color spectrum. Your job is to arrange the caps in each box so the colors flow in a smooth gradient from one end to the other.
Each box takes about two minutes. Errors are scored based on how far each cap lands from its correct position. If cap number 50 ends up between caps 55 and 56, for instance, the error score for that cap is 11 (the sum of the differences from its neighbors). All the individual scores are added into a total error score and plotted on a circular graph. The shape of the plotted errors reveals not just whether you have a deficiency but which type: the error pattern clusters along a specific axis on the graph depending on whether you confuse reds and greens or blues and yellows. A higher total error score indicates more severe difficulty discriminating between hues.
The Anomaloscope: The Gold Standard
The most precise diagnostic tool is the Nagel anomaloscope, considered the gold standard for classifying inherited red-green color vision defects. It works differently from plate or arrangement tests. You look into an eyepiece and see a small circle split in half. One side shows a yellow light. The other side shows a mixture of red and green light that you can adjust with a dial until the two halves appear to match.
People with normal color vision consistently settle on a narrow range of red-green mixtures (centered around a scale value of 40 on the instrument’s 0-to-73 range). Someone with a mild deficiency accepts a wider range of mixtures but still rejects some. A person with complete dichromacy, meaning they’re missing one of the cone types entirely, will accept every mixture across the full 0-to-73 range as a valid match.
The anomaloscope also distinguishes between the two main subtypes of red-green deficiency. People with a protan deficiency (reduced red sensitivity) need more red light in the mixture to match the yellow, so their accepted matches cluster in the upper part of the scale. People with a deutan deficiency (reduced green sensitivity) need less red, and their matches cluster in the lower range. The wider the range of accepted matches, the more severe the deficiency. Anomaloscopes are primarily found in specialized vision clinics and research labs rather than general eye care offices, so most people only encounter one if their initial screening raises questions that simpler tests can’t fully answer.
Testing Children
Young children who can’t yet read numbers or letters need a different approach. The Color Vision Testing Made Easy (CVTME) system uses 12 plates designed specifically for pre-literate kids. The first nine plates contain simple shapes like circles, squares, and stars embedded in colored dot patterns. The last three show more complex images like houses, boats, or animals. Children simply point to or name the shape they see, making it possible to screen for color deficiency well before a child can take the standard Ishihara test. School vision screenings and pediatrician visits are common settings where children are first tested.
Inherited vs. Acquired Color Vision Loss
Most people think of color blindness as something you’re born with, and inherited deficiency is by far the most common form. But color vision can also deteriorate later in life due to eye disease, neurological conditions, or systemic illness. Conditions affecting the optic nerve, the retina, or even the visual processing areas of the brain can all alter color perception. When color vision loss is acquired rather than inherited, the pattern often looks different. Inherited deficiency is almost always red-green and stays stable over time. Acquired deficiency can affect any part of the color spectrum, including blue-yellow, and may change as the underlying condition progresses or is treated.
This distinction matters for diagnosis. The Ishihara test alone may miss acquired deficiencies, particularly blue-yellow ones. Clinicians evaluating patients with eye diseases or neurological conditions typically use broader tests like the HRR plates or the Farnsworth-Munsell 100-Hue test to catch the full range of possible color confusion patterns.
Digital and Online Tests
You’ve likely seen color blindness tests available online or through smartphone apps. These can be a reasonable first indicator, but they come with a major caveat: screen-based tests depend entirely on your display’s color accuracy and the lighting in your room. Traditional physical plate tests require specific standardized illumination to be valid, and even in clinical settings, improper lighting can affect results. A phone or laptop screen introduces far more variability.
That said, digital testing is advancing. A validated digital test called the DIVE Color Test showed perfect agreement with the Ishihara test for identifying red-green deficiency (a Cohen’s kappa of 1.00, indicating complete concordance) and strong correlation with the Farnsworth-Munsell 100-Hue test for measuring severity. Digital tools like this can also test all three color axes, including blue-yellow, and complete the assessment faster than traditional methods. As these tools gain clinical validation, they may eventually replace physical plates in some settings. For now, if an online test suggests you have a color vision deficiency, it’s worth confirming with a standardized in-person test.
What to Expect at Your Appointment
Color vision testing is painless, non-invasive, and usually fast. A basic Ishihara screening takes under five minutes during a routine eye exam. If the results suggest a deficiency, your eye care provider may follow up with arrangement tests or refer you for anomaloscope testing to determine the exact type and severity. No eye drops, no special preparation, and no discomfort are involved in any of these tests.
The results will typically classify your vision as normal trichromacy (full color vision), anomalous trichromacy (reduced sensitivity to one color range, the most common form of “color blindness”), or dichromacy (one cone type missing entirely, causing more significant color confusion). Within each category, the specific axis of confusion, whether protan, deutan, or tritan, will be identified along with whether the deficiency is mild, moderate, or severe based on error scores or matching ranges.