My usual preference is: leggings under white boots; leggings over the boot; leggings under tan boots.
I used to get white boots for rentals! I don't associate tan boots with rentals at all. I don't mind them, but they do indeed look a little less clean. I like neutral tans and browns in general, but the material that is used for skating boots don't seem to make a nice colour for my eyes. I have an awesome pair of tan suede knee-high winter boots
White boots don't necessarily clash with the outfit of a skater because somehow, to me, when a skater is on the ice the white boots are just a natural part of that attire, heh. It doesn't stick out too badly. Plus, the ice is white anyway. Does the skater's outfit now clash with the whiteness of the ice?

I agree with everyone who said that the clear outline of the white boots narrows the ankle and creates a sleek appearance.
I HATED the leggings over the boot look when I first saw it. Sometimes, in close-ups, it still bothers me, especially when there is a bend at the ankle. However, when the legs are straight, it doesn't bother me too badly anymore; maybe I got used to it, but yeah, I guess the neutral-coloured continuity is flattering, too. I still would prefer to see the skates clearly on the skaters, however. I did not know that skaters intentionally did the stocking thing to try to "lengthen their lines" - I agree with everyone who comments that the knobbly look at the ankle is both unsightly and breaks the line anyway.
I admit that this looks very nice:
http://www.jewoftheday.com/Ulpan/Images/Sasha Cohen.jpg
However, I think she'd look fine anyway with no affect on her lines with white boots:
http://www.laurenpfiffner.com/images/sasha2.jpg