I like yellow/amber, especially on overcast days. On bright sunny days, I'm wearing polarized sunglasses.
Yellow is the brightest color to the human eye. I'm a photographer, and when shooting black and white film, a yellow filter gives you a slight boost in contrast while an orange filter will give you the most contrast of the color ranges. Thus, for our purposes, amber gives the best balance of the two. While brightening the perceived image and adding contrast, our eyes can quickly determine targets/silhouettes as we jump from one to another, or are looking for holes on paper.
Whether amber gives you much of an advantage in a combat scenario--I can't speak to that because I've never been there, or done that. On the range, however it is an advantage *as long as* it's not too bright out that your eyes are taking in too much light to operate effectively. I believe in such a case (and going back to the photography side of things with light), a neutral density (sunglasses), or polarizer (polarized sunglasses) help keep your eyes operating the best they can.
*Edit: color or shade aside, the only thing that will negatively effect you if using glasses with optics is the optical clarity. Using crappy $5.99 gas station glasses will not only damage your eyes by making them strain through a distorted picture of the world, but it will possibly (and likely) distort your perception through quality rifle optics.
There's no point in buying a $4k Schmidt & Bender, and looking through it with the gas station "bro" sun-g's.
Footwear and glasses are the two things I will not cheap on, emphasis on the eyewear. You only get one set of eyes in this life :) Pony up for some quality lenses.