So the other day, I started playing Crush Roller and totally got hooked. And then I remembered that there was this God-awful bootleg of it called Brush Roller on the Famicom. I then got the brilliant idea to fix the color palettes and the sprites, given that those were the majority of the problems with it, and essentially have a carbon copy of Crush Roller, ready to go on my NES.
However, it's now dawned upon me that there are some issues with the palettes (seen below in the screenshot, particularly with the cat and mouse) and they're starting to bother me.
So is there any real way to expand the palettes of a ROM and add in some more colors?And on that note, is it also possible to add in completely new sprites/frames of animation instead of just reworking the graphics, like the majority of tutorials show you how to do?
Well, yes and no. There probably isn't a cookie cutter solution to this problem. Likely, you'd have to learn some NES machine code (assembly language), reverse engineer the game's code, then figure out how you can rework it.
You can't normally expand the size of the palette in the Famicom. There are 32 palette entries with 7 unusable ones (12 sprite, 12 background colours, 1 backdrop colour and 7 normally unusable entries) in the Famicom's Video RAM and you can not expand this. In other words 25 colours can be displayed at once on the screen. With some trick you may be able to simulate more by flickering somehow, but I don't know how good that would look or how to do it.
You may change the colours in the palette entries though (the Famicom can generate 52 different types of colours plus a glitchy one that should not be used). That game doesn't seem to use a lot of colours though so I bet it's possible to colourize it much more and clean up the ugliness. The game seems simple enough that you would probably "just" need to change the character pattern data (it's in the CHR-ROM) to add more colours and also change the palette data (it's in the PRG-ROM) the game uses to match the changes in the pattern data.
So yeah probably no cookie cutter solution, but you might get away without needing to know how to program, as long as you know where to look for the data. I can program assembly a little but I'm no good with hacking so I can't help you there.