[MENTION=18111]Bighead[/MENTION] - If you're interested, there is an HD build of GBE here ->
http://www.emutalk.net/threads/55007-GB-Enhanced?p=452812&viewfull=1#post452812 About Kirby's Dream Land, watch out for solid colors! Specifically the trees in the first level. The insides have the same pixel data as other parts of level 2 (the mountains in the background). I guess going for green mountains or fall-ish brown trees would work.
FYI for everyone else, I'm working on GBE+ at the moment, which will basically replace GBE. I expect that the format for custom graphics will remain the same and compatible with GBE 1.0. Anything that's new (GBC and GBA custom graphics) won't affect what GBE can already do, as far as my tests show anyway. Obviously my biggest focus is getting GBA support somewhat functional before I integrate GBE's old codebase and begin work on the GUI.
Great work Bighead, I played this the other day and I really had fun. Maybe I'll work on colorizing stuff myself