I don't see why using other solid colours would necessarily be unintuitive.
If you use a different combination of colours, i.e. primary colours such as blue, yellow, red. Then you could use combinations of these colours to produce secondary colours based on the logic of mixing those colours to represent each combination.
I would suggest using RYB as the primary colour scheme here, because I think most people will be at least semi-familiar with this from learning to mix these primary colour paints at school, when they were children.
For example
