Clear as white gets my vote, but you could make just as much of a case for going the other way.
Personally, I find that kind of ambiguity unsettling, and I never liked playing with my glass chess set much. My eyes and brain are a lot happier since I retired it to a display case and bought a more conventional set.
The rules I read once said that White is the lighter color. Between Green and Purple? Lol. I just had a thought, you could make Green White this game and the next game make Purple White. 
I've been pondering this question for over 10 years!
Recently a lively grandson accidently knocked the frosted Queen on to a stone floor, with shattering consequences!
I collected the pieces (well, some of them!) and am in the final stages of re-constructing the Queen. When it is completed I will paint a ceramic spot of colour on the tops of all the frosted pieces.
The spot will be white (or maybe black!), but then everyone will know for sure which side they are on, and one of life's many uncertainties will have been eliminated! 
If people can't figure out which one is White and which one is Black, then something's wrong with the basic design.
I would say frosted would be white since it's lighter color, but this is why I don't play with that kind of glass set.
Doesn't really matter as long as "white" moves first.
I'm just curious. When playing with a glass chess set, which side is White: the clear or frosted pieces? My glass set has clear and milky-frosted pieces and board. I used to think that the clear pieces were White because they were transparent and the frosted pieces Black because they were opague. Clear was the lighter color in my mind. On the other hand, I can see the point that the frosted pieces are White because they are have a whitish milky color and the clear Black because that is the other side's color. What do you think?