Why blue is nearly invisible on terminal emulators

Benjamin Sago writes on a problem of distant youth: the almost invisible blue displayed by terminal emulators restricted to the classic RGB pallette of those ancient machines. A particularly lethal NetHack monster is rendered with that blue, creating a problem for would-be adventurers. "It turns out," he writes, "the bug is in our eyes."

Each RGB pixel on a computer monitor emits a certain amount of red, a certain amount of green, and a certain amount of blue, depending on which colour it's showing. Human eyes, on the other hand, are not neatly subdivided into red, green, and blue cone cells. We have L, mostly for greenish yellow, M, mostly for yellowish green, and S, for blues and purples. They overlap to varying degrees, and some colours (wavelengths) of light will make all three cone cells respond

Pallettes generated using RGB channel flags (each channel on or off) often have the same problem: you cover the color gamut in a technically elegant and concise way, but in reality it looks weird because that's not how we perceive color. I grew up with the Amstrad CPC, which while having a lot of colors for an 8-bit (The 27 generated by 0%, 50% or 100% RGB channel intensities) a fair third of them were oversaturated green-tinted gaudities. And only one single color might fairly be described as dark: the blue.