You could always use another CB client.. The one I use has them in the normal flow of CB text, but in red. Katterbox also does something similar, I think.

As for PM itself, the most you're probably going to get is the messages each with their own class set, so you can style them yourself.. Unless you'd like to go through all the available themes on PM, and suggest a suitable colour for each, in which case someone might actually change them.. If you're lucky.

C.