I have "jade colored" Yunzi which (of course) appear green when held up to a light, but since I don't have the white variety I was just curious if the white stones give a greenish tinge when viewed against a bright light (as the "black" stones are well known to do). Thanks in advance!

yes

I have a fairly new set of double convex size 33 Yunzi from YMI. My white Yunzi do not have a green tint. The black do, but the white are merely somewhat transparent when held up to light.

My white Yunzi stones do not have a green tint.

White is an extremely opaque pigment, so while the composition of the stones should be the same, the light can't penetrate the stone, hence no green glow.

See http://www.reddit.com/r/baduk/comments/74xz9j/what_kind_of_yunzi_stones_are_these_do_modern/
Two kinds of yunzi?

That MIGHT not be the reason. When something looks white to us it means that it is reflecting all colors of light well. What additional small amounts of light might be passing through or scattered internally not going to make much difference. But when something appears black to us it means that it is not reflecting light. In which case a little bit of some color passing through or being internally scattered quite visible.

Simple test. Mount stones of each color in a hole in cardboard just smaller than the stone and place a bright light behind (with your side of the cardboard in the dark). Report on what you see for back and white yunzi stones << the test just eliminated reflected light in both cases; so we only see what is transmitted/scattered >>