Yellow
Diana's skin is the wrong colour. Where it should be a smooth, unbroken bronze it is instead sickly and jaundiced. The center of her face is a nauseating shade of yellow-green and Faye can't stand to look at her. She did this. Her stupidity is written all across Diana's face and she just can't stand to look at it.
She turned away when Diana tried to kiss her earlier, flinched back when she tried to hold her hand. She doesn't want to see what she's done. She isn't in denial- she's not that stupid- but she just can't bear to see the wreck she's made of her girlfriend's face. She has no trouble looking at her own swollen eye (that was her own fault, afterall) but there's something about looking at Diana's bruises that makes the guilt sharp enough to cut.
She doesn't understand that her turning away is hurting Diana more than any bruise. That punishing herself for a mistake is a pointless exercise that's doing nothing but hurt them both. So she'll bit her tongue and wait for the day Faye won't turn from her, will let her kiss her how she usually does.
She just hopes it'll happen soon; the wait is killing her.