Glasses, even photochromic ones (those that get darker in bright conditions and lighter in dark conditions), are going to be optimal in some conditions and in others not so much.
These are just general places to start from as companies vary.
Gray for the brighter bluebird days. VERY easy on the eyes. If you're prone to ending up with a headache it's a great lens. Not ideal for cloudy days, but especially on brighter cloudy days it's still the choice for many. Natural coloration of what you're seeing. Popular for offshore fishing.
On cloudy days copper, brown, amber, etc come into their own. These offer heightened contrast and generally these allow a little more light in then a comparable gray lens. Many feel copper offers the best contrast but it's a "harsher" lens tint for some people, occasionally even resulting in a head ache for some or tired eyes at the end of a long day. Brown offers most of the contrast with the almost none of the harshness some find in copper. These lenses are seen in use everywhere, but certainly in flats fishing scenarios for heightened contrast.
Rose, yellow, etc. Unless they are unusually dark most consider these to be low light lenses. Great for cutting glare (assuming they are polarized) on those foggy mornings when the sun is starting to cut through the fog. Some people even drive with a pair at night to kill glare (myself included) as some lenses filter out almost zero light. Usually not the glass people buy first and with good reason but once you have a pair you'll miss them when you don't.
As for "mirror" finish, sometimes but not always this is more for looks. Sometimes it will add a hint of blue or green. It MAY lower the light transmission percentage a few degrees, or not. Far more important is knowing what lens that mirror film is attached to more then the color. If "blue mirror" has a gray lens, expect it's predominant lens qualities to be that of a gray lens.
There's a million gradations in between those general colors as well half of which are different names for the same thing between various companies. And then add in personal preference. You almost might as well suck it up and buy several pairs and get it over with.
