GBcolorizer is the only one I've personally seen, and that one has lots of problems even with the MBC1 ROMS it claims to support. Development on it just ended abruptly, from what I could find, with no hope of any future updates.
You are indeed correct. I had the privilege of being in contact with Blind Tom for most of the early work on GBColorizer; he even liked my Metroid II colorization enough to include it with the program's distribution. Unfortunately, like you said, all of a sudden the guy just up and VANISHES. And I mean, poof, gone. Never went onto his IM again, never updated his page again, and never replied to any emails either. It was like all of a sudden the guy just ceased to exist. Eventually Geocities removed his page from lack of use, and the program along with it. I've tried to find the guy since then, but with no luck.
It's been years since then, and yet... were he to pop up with a new version, I could jump right into it and start colorizing again. *sigh* We all have dreams, I guess.