Your suggestion and question go nicely together...
Think of
Advanced Search as a full-feature custom filter—there really isn't any difference (in the end result) between a search and a filter. Unfortunately, a search can't be applied as easily as a filter. Someday, I hope that's rectified by adding some sort of mechanism for saving custom searches, and making them available in a menu.
Now if such a feature were in place, the same saved searches could be used to specify custom list colors. Regardless of how it's implemented, the problem with custom colors is an item can only be
one color (i.e., how should a seen DVDRip be colored?). It quickly becomes tedious and confusing if new criteria overlap with existing ones. At least using a saved search to specify precisely the criteria for each color would help. It would also allow the color scheme to be simplified. For example, you might decide you care about whether or not an item is a DVDRip only for unseen items, so the rest could be left in the color for unseen items.
All this is mute if using advanced criteria would slow down the display of the list. If that's the case, but a simple criteria would not, I suppose the next best thing would be to make the order of the color "rules" significant. Each item would be colored according to the first rule that applied, and subsequent rules would be ignored.
This begs another question. If the saved search feature existed, would we still care about custom list colors? I realize it's not the same thing, but if I can instantly filter my list to any criteria I want, I'm certainly going to care somewhat less about those items being distinguished by color. What do you think?