Would be really nice if under the advanced search, while viewing inventory or database, the color options were more robust. It would be nice to have an option for multi-color, mono-color, and hybrid. Also the ability to require certain colors in a search would be nice.
You should already be able to able to accomplish everything mentioned here aside from a search for every multi-color card exclusively. You can change the search type and select more than one color at a time to do almost anything.
If that doesn't answer your question, would you please provide more specific examples?