Since you need to define if a sprite is MC or Mono from the outset, that's not an easy feat. You'd have to analyse pixels, figure out what is worth making into MC mode as well as considering the 2 global colours so that all other sprites work with the same mindset... that is not very straight forwards nor convenient to code. So, ultimately just call each sprite Mono, you can then stack them how you want. Or just be more methodical about how you combine MC and Mono colour sprites, that's the technical part you are hoping a tool to solve for you, sometimes you just need to think about it for yourself as a kind of challenge of limitation.
Thanks for the suggestion, but I don't think that's a fair order lol.
Viewing post in Spred64 - C64 Sprite Editor V1.44 comments
Ok, I just didn't explained it good enough. I know that you need monocolor sprites and layer them. The idea would be, that you can pixel it, like there is no limitation, example using 5 colors same time. Finally, the tool would examine how much sprites it would take.
It's ok, if you don't like the idea and not able to do it. But a lol isn't needed in this case.
I saw a C64 sprite editor that can do that. https://csdb.dk/release/?id=143682