The answer depends on which plasma you mean. Blood plasma, the liquid portion of your blood, is a pale yellow fluid that looks similar to straw-colored water. Physical plasma, the fourth state of matter, is a glowing ionized gas that produces the light in stars, lightning bolts, and neon signs. Both share a name but look nothing alike.
Blood Plasma: Pale Yellow Liquid
If you’ve ever seen a tube of blood after it’s been spun in a centrifuge, you’ve seen plasma. The spinning separates blood into distinct layers: red blood cells sink to the bottom, a thin whitish layer of white blood cells and platelets sits in the middle, and plasma rises to the top as a clear, pale yellow band. It makes up about 55% of your total blood volume, so it’s the largest single component.
Plasma gets its yellowish tint primarily from bilirubin, a pigment produced when old red blood cells break down, and from dissolved proteins. The consistency is slightly thicker than water but much thinner than whole blood. On its own, it looks like watered-down apple juice or light chicken broth.
When Blood Plasma Changes Color
Healthy plasma is consistently straw-colored, but several conditions can shift its appearance noticeably. These color changes are one of the first things lab technicians look for when processing a blood sample, because they signal something unusual going on in the body.
- Pinkish or reddish: This happens when red blood cells rupture and release their contents into the plasma, a process called hemolysis. It can result from a blood draw that damages cells or from an underlying condition like hemolytic anemia.
- Greenish or brownish: Elevated bilirubin levels, often from liver disease or jaundice, tint plasma in this direction. The more bilirubin present, the deeper the color.
- Milky or cloudy white: High levels of fat particles in the blood, known as lipemia, make plasma look turbid and opaque. This turbidity becomes visible to the naked eye when triglyceride levels exceed about 300 mg/dL, which can happen after a fatty meal or with metabolic conditions.
If you’re donating plasma and notice it looks different from the usual pale yellow, that’s not necessarily cause for alarm. Hydration, diet, and medications can all temporarily affect its appearance.
Physical Plasma: Glowing Gas
The other kind of plasma is the most abundant form of matter in the universe, making up stars, nebulae, and the thin gas between galaxies. It forms when a gas gets so hot, or absorbs so much energy, that electrons separate from their atoms. The result is an electrically charged, glowing substance that behaves differently from ordinary gas.
The key visual feature of physical plasma is that it emits light. Unlike a solid, liquid, or regular gas, plasma glows because its energized particles release photons as they interact. You’ve seen this many times without necessarily knowing it: the bright flash of a lightning bolt, the shimmering curtains of the northern lights, the colored glow inside a neon sign, and the surface of the sun are all plasma.
Why Plasma Glows Different Colors
The color of a plasma depends on two main factors: what gas is involved and how hot it is.
Different gases produce distinct colors when energized into a plasma state. Neon gas glows red, which is why classic “neon” signs have that iconic warm color. Argon plasma glows violet. Xenon produces blue light. This is why signs advertising different colors aren’t all technically neon. They use different gases (or phosphor coatings) to achieve the full spectrum.
Temperature also plays a major role. As plasma gets hotter, it shifts from reddish tones toward blue and white. A blowtorch flame follows this same principle, turning from red-orange to blue as you increase the heat. Stars work the same way. Our sun, with a surface temperature of about 5,500°C, appears yellow. A cooler star like Betelgeuse, at around 3,000°C, looks reddish. A much hotter star like Rigel, at roughly 12,000°C, burns blue-white. So when you look at the night sky and notice stars of different colors, you’re seeing plasmas at different temperatures.
Everyday Examples of Plasma
Physical plasma is easier to spot than most people realize. Fluorescent light bulbs work by running electricity through a gas until it becomes plasma, which then excites a phosphor coating to produce white light. Plasma TVs (now mostly replaced by LED screens) used tiny cells of ionized gas to create each pixel. Welding arcs, the bright spark of a lighter’s piezoelectric ignition, and even the brief flash inside a microwave when you accidentally leave a fork in there are all small-scale plasmas.
On a larger scale, the aurora borealis forms when charged particles from the sun collide with gases in Earth’s upper atmosphere, energizing them into a plasma state. The rippling green, pink, and violet curtains you see in aurora photographs are the visual signature of different atmospheric gases (mainly oxygen and nitrogen) being excited at different altitudes. Ball lightning, a rare and poorly understood phenomenon where a glowing sphere floats through the air during a thunderstorm, is also plasma.