Monocolored creatures can't block this turn.
4/15/2013 A monocolored creature is exactly one color. (Colorless creatures aren’t monocolored.)
4/15/2013 No monocolored creature will be able to block that turn, including monocolored creatures that enter the battlefield after Awe for the Guilds resolves. A creature that’s monocolored when Awe for the Guilds resolves but somehow becomes multicolored before blockers are declared will be able to block.