As Jay Wilson, lead designer on Diablo 3 announced in an interview that there will probably be no major changes to the "bright colors" in D3.
He was with the critical D3-petition ("darker power D3") and some screenshots confronted, he also commented the same. All images were post-processed with Photoshop and in this appearance not at all technically feasible. Excessive Licht-/Schattenspiele consume in a 3d game just too many valuable resources. Since D3, however, is to run on older computers, such was quickly discarded.
Other Fan Pics would by lack of contrast, too confusing, since the Spielchars barely stand out from the background, so Wilson.
When you pull all the color out of the environment and you make it too homogeneous across the game, Essentially what you're doing is you're pulling away the player's reward of feeling like they've Progressed Because The area they're in now looks like the area theywere in 30 to 45 minutes ago.
OK, that's very clear. As it stands, Blizzard will not be put out of the nearly 50k signatories of the petition and continues to pursue its course.
Source: Interview on MTV Multiplayer