The color red
The color pure red is a particular frequency of light. It makes no difference whatsoever if your brain perceives it differently than mine--red is still red, and anything in the world that is red will be identified as that color by anyone with normal vision.
Be wary of anyone trying to convince you that objective reality doesn't exist, and that everything is fluid. They usually have a reason for trying to do so, and it's rarely an intellectually healthy one, either for themselves or you.
One cannot even say "there are no absolutes" without expressing an absolute.