Light

The teen has a physics exam tomorrow. He missed taking it with the rest of the class because he was away with his business English course, this means he knows what was covered in the exam*.
One question involved a bus (or maybe a train - I wasn't paying too much attention) travelling towards a guy at 0.9c (where c = speed of light) what colour are the lights on the vehicle that the guy sees (before he's squished as flat as a pancake)?
When Little miss bossy heard this question she informed us that she wouldn't be studying physics....

* although clearly he wont get the same questions.