Three dimensional colour map in python

Question

I would like to visualise a competition between three different processes in python. The figure should show the relative importance of each process at all grid points. My idea is to make a contourf plot with a colour map that has three extremes, for example red, green and blue. Every extreme would be assigned to one of the three processes and wherever several processes play a role we would see a mixture of the colours weighted by the relative importance of the processes. Does anyone have an idea if/how this is possible? Thank you very much!