UBB.threads PHP Forum Software Community Forums UBB.threads 7 Version 7 Support Shout box alternative shades

OK I am trying to get it so that 2 colors are used in the Shout Box - each alternative post having a slightly different shade.

I've been trying for ages but unsuccessfully.... which part of the styles will that be in (I thought it would be left/right column but it doesn't seem to be),

Thanks