My wife and I each have a pair of Manifest goggles that I bought at the end of last season to go with our new Omen helmets. Of the two lenses, one is clearly an amber color which I assume is the Gold Boost lens and works well in overcast or low light conditions. The other one, which I assume is the Rose Silver, is noticeably darker and works fine on sunny days. Before I got on the slopes I didn't think this lens would be dark enough but my eyes are a little light sensitive and it's been fine on days with bright sun.
I really like the ease with which you can quickly change lenses. I've skied with them at various resorts in Tahoe and Utah this season. In Tahoe we had heavy overcast/fog and/or storms for the first three days and the amber lens worked better than my Habervision goggles with the Optic Orange lens, which I found too dark. When the skies became mostly sunny/partly cloudy for the last three days, I was able to easily swap the lenses in less than a minute on the lift or at the top of a run to adapt to changing light conditions. The extra lens fit easily in the goggle pocket of my jacket below my armpit and fit the curve of my torso.
I was also disappointed that Giro doesn't seem to have any other lenses, even though there are indications that you can get replacement lenses. My e-mails to Giro went unanswered. IMHO, they have extremely poor customer service.
In hindsight, while I like the Manifest goggles, I wish that I had looked into the Smith IO goggles before I got the Manifest. Smith offers a whole range of lenses for the IO and you can even buy them on Amazon.