The red on the rear of the cab does look unsightly, but looking at the transformation in the cartoon where the colour just magically morphs from white to red, I think it's understandable.

Whoa, I didn't know that his face expression was changeable! According to the text caption below the photo of the open mouth, it's to recreate the scene from TFTM when Ultra Magnus is attempting to open the Matrix! So it's his expression as he's being terminated by the Sweeps -- ouch! Pretty morbid considering that the only time Magnus' mouth is gaping wide open like that during that scene is when he blows up! (prior to that, he just looks and sounds constipated ) In the Marvel Comic adaptation, he has a similar expression at the moment when the Sweeps tear him apart!