Could be 'Dreamhunter' by Elizabeth Knox? It's got a dream-related plot and there's this whole Dreamhunter Duet series. Worth a shot?

If it's not 'The Lightbringer Series' by Brent Weeks, then my second guess would be 'The Black Prism', start of the series. The color magic thing is a dead giveaway. Super epic with a capital E.