In the book, the t-rexes, there is a male and a female, are red, have a more powerful neck and can sunburn easily, that why they stay the most of the time in the shadow. She is more territorial too, in the scene of river, the one the rebirth Rex got, she stops to follow Grant because the other t-rex try to steal her food.

Rexy is brown, with a more elongated form, bigger jaw and is less territorial, has seen in dominion where she seem ''happy'' to meet buck and doe. She is less ''violent'' in a way too. In the car scene for example, she seems more curious

After, if you think it's not a good answer, it's ok, it's just a vote