Over and under is a fatuous debate...
If it's over, then without even touching the roll, all you have to do is flip the paper holder 180 degrees horizontally and it becomes under... and vice versa... so the debate is not over or under but right or left, and the simple answer is to put the holders on a pivot... (I know, pretty shitty reasoning!)
As to color, it would be very hard to find the right color brown that would equally camouflage all the colors likely to be found in a toilet bowl! Maybe toilet paper manufacturers could learn from the chameleon and make paper that changes color to match the situation...
Any other questions?
Perry