Deer or other hoofed animals don't see much in the way of color, so shades of gray are fine. So are other contrasting patterns with a variety of colors. For instance, I think ASAT and Predator camo patterns are generally the best for deer, but ASAT is not good for spring turkey hunting.
This last spring I was turkey hunting using my ASAT leafy camo suit. The deer never saw me unless I was moving, and even then they had trouble seeing me as long as I moved slowly, despite the fact that everything around me was mostly green. But when I was sitting absolutely still in the middle of green vegetation where deer didn't look at me twice, the turkeys stopped dead in their tracks 70 yards away, refused to come closer, became really agitated as they tried to figure out what I was, and then took off when they decided I was out of place. They obviously spotted me because of the color of my camo, because when I went back to camp and changed into my Predator camo with green in the pattern, the turkeys that came to my calls later didn't spot me as long as I didn't move. Unfortunately, I shot at a moving turkey 20 yards away that stopped walking just as I was releasing the string. I shot just ahead of the turkey and it (and the others with it) ran off. But none of them ever saw me; that one just saw an arrow passing a couple of inches in front of its chest.
In my opinion, the Predator fall gray pattern and the ASAT pattern are fantastic for ungulates at any time of year and great with turkeys in the fall season. They are both incredible in treestands in the fall where there are no leaves. Another pattern that is the absolute best in treestands in the late season is Skyline Horizon camo.
http://www.skylinecamo.com/pattern_results.php3?idkey=14 Horizon is unbelievable in a tree during the late season or in snow anytime. When my friends are sitting in a treestand wearing Horizon, I can't find them unless I know where they are sitting and get up close to them. Same thing in snowy conditions. The coveralls can be reversed from the Horizon pattern for treestand hunting to the Apparition pattern for ground hunting. Just order a larger size to go over all your other bulky late season clothing. At $80 it's a bargain, and you don't have to worry about what colors your underlying clothing is unless you take off the coveralls.
Lots of other patterns are great too for other environments, like the Cabela's Outfitter camo. It's like matching the hatches in flyfishing. You just have to remember that fish and turkeys see various colors and deer and other ungulates don't, so shades of gray work well for ungulates while turkeys require color matching too.
Allan