Hi Russ,
I don't think I've ever seen that. I tried it on 10.5.8 and it worked as expected.
Just to be clear, does this happen when clicking a colour button in a node parameter view?
Do you get two TG2 colour pickers? I'm presuming you know what the Apple one is like.
The only thing I can think to suggest is trashing your TG2 preferences. In fact perhaps trashing them is a bit strong considering I'm not sure if it will help. It might be best to rename them, restart TG2 and see if it helps and if it does then trash the old prefs. You can find the preferences in:
Your user folder -> Library -> Preferences ->
uk.co.planetside.Terragen_2.plist
Rename the file to something like "uk.co.planetside.Terragen_2.plist_old". If you restart TG2 and it works properly then throw that file away. If you still get the double picker then trash any new preferences file created and remove the "_old" from the old preferences file.
BTW, I'm not sure if I mentioned this to you before but TG2 renders quite a bit faster on OS X 10.6 if you have a multicore machine. I definitely recommend people upgrade to 10.6 if possible.
Regards,
Jo