Many lenses like Gold Iridium, Black Iridium, etc, are pretty much sunny day only lenses. They filter too much light, and when it gets darker it becomes harder to pick things out. Essentially, the lens is no longer working as it was designed to. HI Yellow will straight up blind a person unless the sun is down.
Pink Iridium, along with HI persimmon, allows the right amount of light through to allow the skier to see a clear image in a variety of conditions. It is great for grey bird days, because it will not blind you but it is still tinted enough to improve depth perception. At night it is also still good, because what you see is so close to identical to the real thing. It can also hold its own on sunny days, it will be brighter than many prefer but it does protect your eyes somewhat.
Basically its a great go between lens, because if you can own only one lens, this is one of the few that will hold its own 24/7 in all kinds of weather.