The Difference Between Red and Green

I almost died laughing during Abstract Algebra today:

Teacher: "...one is green and the other is red so there isn't much difference"

Important observation: Teacher is COMPLETELY colorblind.

My thoughts: "I know what he means, but to him, there is NO difference, and to me, those colors seem completely different... either way, the analogy doesn't work."

(I knew he meant very there is very little difference. And on another note...)



In your opinion: Is there a big difference between red and green? What if there is another context, like there are two cars exactly the same except one is red and the other is green, then is there a big difference?