AbleGamers has a conversation with Jeff Kaplan about the upcoming accessibility changes to the game in patch 3.1. We saw in the patch notes already that there would be a new colorblind mode added to the game, but Kaplan goes into more detail here -- Blizzard is making sure that even when the interface depends on color to get information across (as in, how difficult your quests are or whether you'll get a skill point from making a crafting recipe or not), there will be other text and symbols in there that relay that information without color.
Unfortunately, while the changes that are going in the game will be helpful. AbleGamers points out that the game isn't perfect for those with colorblindness yet -- mob levels are often shown to the player in a certain color, and there's no option yet for players to see that information in any other format. Additionally, Rogue combo points are shown by filing those little circles in with colors, and colorblind players who aren't able to see that color will have difficulty with that mechanic as well.
The good news is that, while Blizzard does want to make sure their core game is as accessible as possible, there's lots of room for addon authors to do more. Colorblindness is surprisingly prevalent, and everything coders can do to make the game easier to play will be welcomed by those who need it.