In Fast & Furious aka The Fast and the Furious 4. When Dom is out on the road piecing together Letty's accident in his mind... how does he know the color and make of the car she was driving? He obviously wasn't there.
You're right, he wasn't there when the crash or subsequent shooting occurred.
During the scene in question, Dom was at the crash site putting the pieces together, I'm not convinced he would have cared what colour the car was. For the sake of the viewer though, rather than narrate what he thought was happening they showed a scene with Letty's car flipping over, since this was shown in a scene and "colourless" isn't possible, the car had to actually be a colour. This scene is purely for the viewer.