When you say where text is greater than 0, I'm assuming you mean that you want to exercise this function on a numerical field.
If so, there are a couple of ways available to you.
If you're using Crystal 8.5, you can right click the field, and select the Highlight Expert, which enables you to specify what colours to attribute to a field depending on the value returned.
If you're using an earlier version of Crystal, you should right click the field, select Format, Font, and hit the x2 Conditional Formula button next to Color.
Then type: if {Your.Field} > 0 then red
You don't need to use numbers to refer to colours in Crystal. But, for the record, I think red is 255. Crystal recognises either format.