[alfons_foobar]

That's a funny idea :)

I think the first one should be very much doable, but I am not sure how I would build the "almost complete" and the "similar colors" features.

[yesbabyyes]

I guess calculating the Levenshtein distance between the sets would work somehow?

Edit: scratch that, just intersect the set of available pieces with each set. If there are fewer than n--or m%--missing pieces, suggest those.