RGB
Additive color: screens build every color by mixing red, green, and blue light. All three at full blast makes white.
See it
What it is
RGB is how screens make color: three tiny lights per pixel, red, green, and blue, mixed at different intensities. It is additive, so adding more light gets you closer to white, which is the opposite of paint and the opposite of CMYK ink on paper. All three off is black, all three at full is white, all three equal is gray.
Each channel is usually written 0 to 255 (8 bits, about 16.7 million combinations) or as a percentage. In CSS you write rgb(79 70 229) with an optional alpha, and hex is the same three numbers in base 16. RGB is a model, not a specific set of colors: the same three numbers mean different physical colors in sRGB, Display P3, or Rec. 2020, which is why a color space always tags along in serious color work.
Gotcha: RGB numbers describe the hardware, not your eyes. Doubling every channel does not look twice as bright, and averaging two sRGB colors channel by channel produces a muddy, too-dark midpoint, which is the classic reason a red-to-green gradient goes through swamp brown. Fixing that means blending in linear light or in a perceptual space, not in raw RGB.
Ask AI for it
Specify these colors as RGB channel values in the 0 to 255 range and explain the mix: give me the rgb() value for each swatch, its hex equivalent, and an rgb() with alpha for the overlay variants. Then produce a red-to-green gradient that blends in linear-light rather than gamma-encoded sRGB, so the midpoint stays bright instead of turning muddy brown, and show both versions side by side.