
The jp T-rexs have different colors becasue of there sex, the green is male, and the brown is female, the black t-rex in jw, i have no idea why its black, probly cause the scientists made him that color

The one in the trailer that has the i-rex running from an explosion, the goat seen as you see the people cheer at the rex, if you look closer, it has black skin color, it could be just the cgi not finish yet, but still

That T.rex is not black, it's just shading from the trees. Her hide is brown mixed with grey.
@JurassicWorld, the male T.rex in TLW is actually green too. A darker green with dark striped, yes, and I understand it's hard to tell because of the night scenes and the lighting, but he is green. The JP3 male was made a lighter green to indicate that it's not fully grown.

Camoflauge and Gender is the two most apparent reasons I could think of.
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