You may recall me writing about DB::Color a few years ago. That module let you do this with the debugger:

It has some issues, including the fact that syntax highlighting Perl code is, um, not always perfect, but it does the job. The main drawback, however, is that it runs about as fast as a sloth with a spinal injury. It was so bad that even I stopped using it, and I love the damned thing. Today, I may have fixed that.