Human eyes are more sensitive to slight variations in green than other colours. This is why YUV video often encodes green sharper and why 16bit colour give 6 b

Human eyes are more sensitive to slight variations in green than other colours. This is why YUV video often encodes green sharper and why 16bit colour give 6 bits to green and 5 bits to red/blue. So on a circuit board with subtle green-on-green variations, it makes sense that they picked green. But since people have many more rods than cones, black/white contrast is easier to discern and white uses all the subpixels in your display to maximize luminance. And speaking of subpixels, subpixel antialiasing effectively triples your resolution when displaying black/white contrast. The brain also highlights contours of contrasting black/white. (There's an evolutionary quirk in our blue-sensing cones that allows you to see contrasting blue/yellow better than most combinations too but still not as well as black/white.) So sharp white on black or black on white are typically better suited to human vision if you're trying to discern outlines like when reading text. Black/white also avoids the persistence effects that cones have, where when you look away from a green image for example, you'll see an inverted magenta copy of the image for a second or two.