I wish colorizing a Game Boy game was just as easy as to pick up colors in Photoshop! Unfortunately, depending on the chosen game, it usually needs a lot of code tweaks here and there.
Both Mega Man World 4 and Mega Man World 5 have two different pause transitions in the code:
the one that rolls up/down (default)
another one that fades the screen (used while at semibosses rooms for technical reasons)
Additionally, MMW5 always uses the fade transition when played in SGB (probably to avoid abrupt palette changes). During MMW5DX development, I noticed that this transition is a few frames faster than the rolling one, so speedrunners that play the game on SGB have little advantage!
Anyway, the rolling transition isn't very compatible with how the GBC works, even Nintendo switched from a rolling to a fading transition while colorizing The legend of Zelda: Link's Awakening.
The reason is, we are already using the eight available BG palettes during gameplay. Pause screen needs two additional paletttes if we want to make the new gorgeous colorful icons a reality. So, if we wanted those two palettes, we would have no choice but to replace two of the stage ones, but that would make the game's background look odd during the rolling frames.
For MMW5DX it was easy to fix this: I just forced the game to always use the fade transition. Mega Man World 3, on the other hand, has no fade pause transition in its code, so I had to reimplement it for its DX version.
This is probably the latest big milestone in this project. The game is mostly done at this point, just missing a couple of ending scenes that Kensu is already cooking.If you are curious, we've done this in a month and a half. It really helped that the game runs under the same engine as MMW5, so I was able to ease the hardest task of disassembling and learning how the game works internally.
PD: Don't ask me why Dr. Wily has so many blinds in his fortress.