It would be a good idea if painted set showed up when a specific colour was searched.
For example if I put "Want TW Octane" it would come up with the people selling octane sets. It would also help if people were looking for all colours of an item but don't want to use up one full trade slot, they would just have to say "Want Painted Set" and if people had one of the colours that trade would show up for them.
Alternatively, you could make a new "colour" called any paint, which would work the same. If people said they had one paint of an item and a person was looking for any paint, the trade would show up to them.