This feels awfully arbitrary in nature, to be honest, so I wouldn't necessarily discard an image of, say, a nereid with green eyes, or a blonde dryad just because of inconsistency alone. I feel like if you spot a great piece of art and want to apply it to one of your characters, you shouldn't really be restricted by what the game tells you the appropriate skin colour, eye colour or hair colour for that particular character is and what it tells you is not. Considering the fact that saves are easily modifiable, and custom descriptions are an option, in-game descriptions are more there to aid your imagination rather than limit it. At least that's the way I view it.
But yeah, this is partially the reason I made my portrait pack black and white.