This is a common need and question as TFP12 does not modify colors like FPxx used to do
Its not hard but is extra work....go here to find out from recent discussion in parent s/w to TFP (Envisioneer); and explore/search that forum for other help/tips too
http://www.cadsoft1.com/customercare/viewtopic.php?t=5384&sid=ec782bb1f229d3d006a26c2960cab349