[Nauty] geng with predefined colors

[Christoph Steinbeck]

Dear all, 

I would like to modify the geng graph generator to work with a predefined set of colours rather than just one. 

But despite the old saying that no one needs documentation because the code is obvious, I am having trouble to see whether geng could do this at all and where I could inject this into the code, say, after parsing an array of colours as an argument in the form aXbYcZ which is X vertices of color a, Y vertices of color b, etc.

Any hint greatly appreciated :)

Kind regards, 

Chris