@Helm. Not so much a problem for the artist as the programmer. Brightness is exponential in nature, so when color-balancing you need to adjust for this to maintain the pereceptual brightness level. Then you have the boundary problem; 0-255...some requested adjustments simply can't be done to all colors without overshooting and corrupting the integrity. So you have to figure out how much change can actually be done to each color.

And if you wanna take this problem even further; there is this phenomena where colors approaching pure primaries appear "stronger" relative their brightness. I'm struggling to understand and quantify this effect, and I don't know if there's any colormodels that account for this (if someone has any info let me know). But in general I think the concept of brightness becomes muddled for more pure colors, esp. for red which is a "recent" evolutionary addition to the eye. Try comparing the brightness of pure red to grayscales...it doesn't quite compute.