Show highlighted text in different color

Unfortunately it wouldn’t really work, as what if you selected some text that was highlighted and some text that wasn’t? The selection highlight can only be assigned one colour, so it would fail in this case. The trouble is that the highlight colour is really a background colour, and the OS X text system is set so that the selection colour takes precedence. I agree it’s a bit annoying and have tried changing the settings before, attempting to make the selection translucent or suchlike, but with no joy.
All the best,
Keith