Color
Color is not a property of light. It is what a particular eye, with three kinds of cone, does with light.
Tools
- Color Vision ExplorerCone sensitivity, phone subpixel output and a color band on one light-frequency axis, with a live solver for what a screen can and cannot reproduce.
- LMS Color SpaceA rotatable 3D space with the L, M and S cone responses as its axes, showing the pigment, biological and screen gamuts as solids.
- The Line of PurplesSix interactive sections on why magenta is not in the rainbow, why screens fall short of a real laser, and why leaves are green.
How the eye sees color
The eye has no wavelength detector. It has three cone types, S, M and L, each responding to a broad, overlapping range of light. The brain compares their outputs. Any two lights that produce the same three responses look identical, however different their spectra.
That is why a phone screen can imitate almost any color using only three narrow emitters, and also why some colors it can never reproduce.
Why purple is not a spectral color
Violet is real. It is light of roughly 380 to 450 nm, and a 405 nm laser pointer is the easiest way to see it. Purple and magenta are different. No single wavelength produces them. They appear when the S and L cones are stimulated together with little M, which is a mixture the spectrum never produces on its own.
The L cone has a small secondary sensitivity near 400 to 420 nm. That is why deep violet has a reddish tint, and why the ends of the spectrum can be joined into a circle. Magenta fills the gap in that circle, along the line of purples.
Reference numbers
| Cone | Peak | Note |
|---|---|---|
| S (blue) | ~430 nm | Oldest system, gene on an autosome |
| M (green) | ~530 nm | Duplicate of the L gene, on the X chromosome |
| L (red) | ~564 nm | Peaks in yellow-green, not red |
| Phone OLED subpixel | Wavelength | Note |
|---|---|---|
| Blue | ~450–460 nm | Near the S peak |
| Green | ~520–530 nm | Slightly short of the M peak |
| Red | ~620–630 nm | Placed past the L peak to limit M crosstalk |
Pigments
| Color | Code | Name |
|---|---|---|
| Violet | PV23 | Dioxazine Violet. Look for this code alone, with no PR mixed in. |
| Magenta | PV19 | Quinacridone Magenta |
Color Index codes are printed on the tube, marked Pigment or Colour Index.
Rods
Rods peak near 498 nm and only work in dim light. They carry intensity, not color.