Just use those four-section signals with the bi-color arrows like they use for left turns. They use that set-up right where I work at the Airport Rd/Warwick Ave intersection in Hoxsie in Warwick. I see you don't like red or yellow arrows? (except for the right turn signal). I laugh when I see pictures of mid-west left turn signals and they're just regular ball light signals with a sign next to it saying "LEFT TURN SIGNAL". Wouldn't it have made more sense for them to just use arrows for all three color?