Graph coloring is a vast field, IMHO this would need to be addressed in an extra module.

I was lucky to find a satisfying optimal solution, but only for the edge coloring of complete graphs (like requested by the OP)

This edge-case (sic ;) can hardly be included in your very general module.

And there is no easy generalization, according to WP is the general case of an optimal coloring known to be NP-hard.