I have the Oakley Stockhom google with iridium lenses.I'm looking for an additional lens that will work in other conditions, especially snowy or cloudy days. What color lens is my best option?In addition, how hard is it to change the lenses on the Stockholm goggle?

Blue Iridium works for me in all conditions except night skiing (HI yellow) and very very sunny bright days (black iridium). But there is no situation in which it has felt uncomfortable... If you have this particular iridium you might not need anything else.

They are not the easiest lenses to change (so you probably dont want to try while on the lift) but they aren't completely impossible to swap out. For clowdy or snowy days, the HI Amber Polarized, HI Persimmon, or Persimmon should do the trick.