I thought about this, how customized would you want this system to be though? Would you want the changes on overworld only? Otherwise it'd mean making an extra version of every battle sprite rouletta has! That's over 100 pictures to redraw XD
it could work like, you make anything that would change to basically be transparent or something in a way, just, easily changeable if possible, then the colors would be something to put over, then bam, and if you make patterns, would look a little funny but it would work, and it would add some customizability to Rouletta, plus it would be funny and cool to have diffrent colors on her besides just red, it might take awhile, but it would work
but yea, custom colors might not work, but a selector of colors would, the player just does what ever to change their color, and from a few select colors, they can change the color, like for starters, you could easily just have the options be Red, Orange, Yellow, Green, Blue, and Purple, and as you make the game, you can add more and more colors