For me, it depends on what I'm making.... if I'm making fine chinese teas, I use my chinese teaware. It just feels right.
Otherwise, anything goes. Right now I've got a couple of favorites at home. One is white with the Kanji for tea in black on one side and TEE on the other. At first, I thought it was just another Japanese version of interesting English (which was why I had to buy it!), but alas no... it's the German spelling.
My other favorite is a bit heavier and has a great cartoonish image of a dog with a butterfly on his nose. The 1/3 of the mug, and the interior are plum in color, and the rest is natural.
Both these mugs are also great when I want to ice my tea.
At work, I've got a dark green Tigger mug, that's been handed down by generations of English teachers at my school.