I tried to buy some of these through PSIA, but due to a stuff up with their site setup, I ended up with the brown polarised versions. They do OK so I didn't send them back.
I got some X-500 modulator lensed goggs last season, and liked them but htey got scratched hence my attempt to get some more.
however, I have the box the browns came in, and they have a map of the other lense versions.
The Mod Citrus transmit 66 to 28 % of visible light (that's their range of darkening/lightening), and they are rated for dark snowy days through to bright sunlight. Not for night though.
The mod Vermillian seem to have the same numbers.
So i guess it's just perference as to wether you like orangey tinted goggs or pink tinted (the citrus looks orange, the vermillion looks pink).
Hope that helps. i'm still pondering trying to score a pair of those, although the polarised browns do make everything look rather pretty.