You have my sympathies here, manufacturers over the years have cast in all colours regardless of customer needs, presumably they felt that all collectors would paint the figures.
Given that the choice of colour for the spues is easily able to be changed it does seem strange that there does not appear to be a colour code even amongst the individual manufacturers
I like the idea of generic colours as per PSR, which would mean those who chose not to paint can still assemble 'like' forces.
In your case have you considered coat painting figures to match the plastic colour of a particular force ie all blue for Germans, green for Allies etc??