Travis B. wrote: ↑Fri Feb 20, 2026 3:31 pmThe only colors other than black and white being cyan and magenta? What were they thinking?
It's a purely technical decision. The CGA only has 16 KiB of memory, so with a resolution of 320x200, there's only room for 2 bits per pixel (so 2^2= 4 colours). The CGA itself only has 16 different colours, in the so-called RGBi colour space. That means 1 bit for red, green and blue, and an intensity bit making the colour brighter. Since the CGA doesn't have any colour mapping (it was made as cheap as possible), of the four bits of the colour space, two bits are hard-coded in the two bits in memory, and the two other bits are programmed in different registers. This means that when the register bits are set, this influence the entire picture, whereas the two bits in memory influence the colour of pixels. Now, if you have RGBi, you can pick any two bits to reside in memory, and the other two in registers. You can try all combinations, but the one that IBM choose was having red and green in memory, while blue and intensity are in registers. The cyan/magenta/white/black palette has blue set to on in the register*, the green/red/yellow/black palette has blue off. These two palettes do seem to make the most sense, having red and blue or blue and green in memory gives imho worse results.
*00 in memory is always the background colour, typically black, regardless of the blue and intensity bits.
JAL