3
its all css.
its been forever since I did this, or maybe I just made my version of extcal this way, I cant remember... anywho... in my version all of the colors can be defined via css.
I am pretty sure zhollou wrote it this way, you just have to open up the template and look at the css class, edit where needed.
it took me about a solid week to get my cal looking the way i wanted it to. worth it though.