If you find fic definitely pass it along. It's so rare. The fandom needs more Charlie/Colby love.
Ok, I'm just doing a quick search, and haven't actually read any of these (lately, I may have in the past), but here are some Charlie/Colby ones I managed to find.
-Watching You
-Secret Agent Man
-It Changes Everything
-A Terrible, Horrible, No Good, Very Bad Day
-Sisful Thinking
-Xmas Series
-Dishwashing
-Gleam
-Six Ways To Ring in the New Year
-Calculus is Easy
-Observations
-Studying Them
-The Next Time
-Everything
-Illusions
-Existance
-Therapy
-Watching Fetish
-The Settling Down Type
-A Memorable Evening
-Enjoying the Show
-Paths on the Sea
-Now Come the Night
-Understanding
-Introductions
-Breaking
-Revelations
-The entire comm, red_gumballs
-Storm
-Taquila
-Pirate
-
And wow, I was going through a list, and almost rec'ed one by you :P

OK, I really have to stop the list there, because my lunch is over, but the fics are there if you look for them. Of course, since I haven't read them, I can't promise they're *good* fics, but they're there. :p