I saw a software called Mixbox that make pigments behave like their real life paint counterparts and I would love to have this in Krita. However, the developers of the software claim the only way to implement this new blend mode is if the developers of Krita themselves add it in. I’m not a programmer and I’m sure other artists other than myself would love to have this, so could this ever be done? Is there a better place or platform to suggest this?
“add-on” in question:
tl;dr: No, at least not officially because it’s licence is incompatible with Krita’s.
aw that’s too bad 
but thank you anyway for the prompt response!
Are there any other plugins that have the same effect that are available to krita users though?
A few people wanted to reimplement the mixbox algorithms with a compatible license but I don’t know if that actually went anywhere.
There’s a MR opened that adds spectral mixing, as far as I can tell it’s still WIP:
There are now two people working on including the Spectral.js plugin into Krita, @urzeye (who started and did lots of work) and @rvanwijnen (who is the original author of the Spectral.js code) (both are volunteers). It’s not MixBox, but the expected results are similar (more “real-life” mixing and blue and yellow resulting in green).