> everyone has a different idea of dark gray. There are a few factors causing this: * People have monitors with different gamma curves, and even if you try to

> everyone has a different idea of dark gray. There are a few factors causing this: * People have monitors with different gamma curves, and even if you try to match them slight different output for top white and bottom black. Heck, on bad monitors these things can vary across the screen or if you aren't sitting perfectly head-on. * People are working in different environments so ambient like that they are seeing the screen against (home & office lighting, light from windows, reflections of those off home/office decor, and so forth) will vary. * Peoples eyes vary in a considerable number of ways, even ignoring those with variations significant enough to be considered “defects” from the norm. * These things can all vary over time, over different cycle times. It doesn't just affect blacks and grays: on a simple dashboard I've created pastel colour backgrounds are used as subtle highlights (used to separate things, guide the eye a little, to indicate status of things (though there are other, less subtle, indicators when this is significant), and to just make it look nicer (as coldly objective as I can sometimes be, even I appreciate a bit of effort there)) that are useful (you miss them if they go) but don't want to be attention grabbing. I've needed to tweak the colours chosen because while they did the job on my screens they were too similar or too almost-not-there-at-all on other people's.