Granted, I'm not very girly, but it takes a professional at least an hour to color my hair, not including the drying and styling part. I can't imagine being able to do it in a rest stop in an hour, max, and be back on the road just like that. Especially covering up blond. It's just not that easy to do if your hair is naturally dark, ime. Not to mention that no one's said they saw her do it and there's no cctv of her entering anywhere as a blond and exiting as a brunette that I know of. Plus, it seems to me it would be pretty unusual for someone to color their hair in a truck stop shower. Unusual enough that someone would notice (I realize it's possible someone did notice and just doesn't know anything about the case or want to come forward)
Maybe she did it at Travis's house. There was plenty of time. You would think there would have been some evidence in the bath or trash, but maybe not and I haven't heard any testimony about what all they found in the trash or even if it was searched -- although I'm sure it was.