Being black would make it more desirable, as a straight red deck would have a tough time taking advantage of the card beyond [card]Squee, Goblin Nabob[/card] or a token theme
Examples: Guardian of Faith, Resolute Reinforcements, Abzan Falconer Ratchet, Field Medic transforms when you gain life, bringing back an artefact, and transforms back when you sacrifice a nontoken artefact
(Perhaps you're playing a tribe full of cards like Goblin Ringleader and you're more than happy to trade one for one.) But that's a good baseline to start with
That could be necessary for giving the game some longevity once the initial lure of pure collecting wears off
Inking errors, blotches, smears, and that sort of thing dont tend to go too high unless theyre extreme or on playable cards