Is anyone aware of where to find or implement the Kubelka-Munk function to mix colour like natural paint? Emanuelle Tamponi implemented this function in Krita, an open source project, but I can't find anywhere that this, or a similar method, is shared to 'naturally' mix colours. It may be that it's commercially sensitive or private, but if you don't ask you won't find out!
Feel free to re-use the code we have in krita. It's in calligra/krita/plugins/extensions/painterlyframework. It does need the pigment library as a back-up, but I guess you can easily abstract away from that.
Note however that the code is under the GPLv2+ license. If you reuse the code or the illuminants files your code also need to be GPL.
(for more info, please contact me -- boud@valdyas.org or boud on #krita on irc.freenode.net, I'm the maintainer for Krita).