I would use the background color option. You can use it on either a dimension or expression. The expression can even be on a field that is not even in the current chart. It is a little misleading, when you click on the plus next to your dimension or expression, the items are greyed out. Just highlight the Background Color, Text Color or Text Format you want to affect and hit edit. Here is one of my sample background to change my dimension to highlight yellow.
=if([Procedure Code Type]='CPT',yellow())
You can change font color and make it bold as well using the Text Color like this
=if([Procedure Code Type]='CPT',blue())
Bold on Format
=if([Procedure Code Type]='CPT','<B>')
Hope that helps