I noticed there wasn't one, so yeah!

If you wear a t-shirt under your shirt, do you match it with your under bottoms?

Black tee to black bottoms, yes, or usually.
White tee to white bottoms - not always, depends on the style and whether I have the bottom in white - also white tee under most formal shirts for me.

Other colored tees/tanks -- don't have many in other colors than white or black; have a few blue, denim, orange, gray - I just wear them with a non-clashing bottom shorts/briefs/thong -- or go commando!

I can see how I would want to match if I wore an undershirt. The wife likes to see my chest hairs...