Drawpile 2.3 is gonna add a Pigment blend mode, based on MyPaint's. It makes the paint mixing more "realistic", e.g. mixing blue and yellow will result in green instead of a dull gray.
I know there's some people that are very enthusiastic about this stuff. If you are or know someone that is and got a better curve or whatever to use, give a poke somewhere.
For some reference, these are the curves from MyPaint, the T matrix is to go from spectral to linear RGB and the three other arrays are to go from linear RGB to spectral: https://github.com/mypaint/mypaint/blob/master/lib/blending.hpp#L21-L41
MyPaint has some documentation about it and what I think is a curve generation script or something: https://github.com/mypaint/mypaint/tree/master/doc/spectral
(To pre-emptively answer some things. I'm not into this stuff, your gradients wont tell me anything, just give me numbers and I can check how it looks when I plug them in. Yes I know of the Krita merge request and spectral.js, they're unusably slow because they do like over 80 calculations instead of 10. Yes I know of Mixbox, it can't be used for anything because it's under a stupid license.)