I second that and I think I already made that request here a few years ago. I hope someone will do that one day. FFA is one of the best GB titles and its remakes are inferior. I would also do that myself if I could but I never found a noob-friendly GB colorizer.
There are four approaches to GB colorisation.
1) Emulator level.
Here the emulator will substitute shades of grey for whatever your colour of choice is. This naturally becomes emulator limited and is less than ideal in current space year when everybody is not necessarily on Windows PC for such things any more. This will be the easiest of anything you and closest to any kind of "noob friendly" you will get for random games. That said I am not even sure what vaguely current Windows emulators are available for this sort of thing as it was often a fork or lesser used one that had such functionality.
2) GBC backwards compatibility level.
Here you alter the game's tiles like any other graphics edit and rely on the inbuilt colours of the GBC and its descendants -- the GBC basically does a hardware version of 1) but as it is hardware, and some devs even played to it*, and works on basically all emulators that can play to the inbuilt palettes of the GBC. As hard as graphics hacking is for a given game (which means other than pokemon you are probably in normal graphics hacking realms).
2a) Some people have used other things related to this and the more extended palettes that the GBC can kind of do under some circumstances, sometimes even winding back into 1) for easier substitutions or more variety at some level.
3) GBC conversion.
Make the game be detected as a GBC game and alter the game to take advantage of the perks of the GBC (colours, faster CPU, some more of other things). You are not going to get far without knowing assembly on this one which is pretty far from "noob friendly".
4) SuperGameBoy. Much the same as above but you aim for https://blog.loveconquersallgames.com/post/2350461718/fuck-the-super-game-boy-introduction
Naturally this requires a supergameboy (a rare and hard to come by piece of hardware that is not generally portable), an emulator that handles it (rare outside the PC) and is probably less capable than the GBC for the same amount of effort -- other than single device two player (and I do like SGB bombermans, right up there on the list they are) it is weaker in basically every way.
*4 kinds of GB/GBC ROM.
1) GB and made long before the GBC was even a specification. 1a) might be aimed for the GB and had no official GBC extras but knew about the inbuilt palettes to adapt accordingly.
2) GB backwards compatible but had GBC extras.
3) GBC only, would not work on GB (and there was an interesting hacking attempt a while back around here to try to bypass the checks and see what goes... cartridge tilters have nothing on this) and took advantage of the extra grunt the GBC has.
4) Supergameboy compatible.