since conditional formatting affects the whole field...
the best trick I have heard for this is create several formulas that iterate each part that you want: before the highlight, the highlight, after the highlight. Then you can combine all 3 formulas into 1 text field. Now you can change the color on the highlight section and it all should display as desired.
I haven't tried this myself, DBlank used it as a solution, but being as it was so slick, I filed it away as a useful trick should the need arise.
HTH