Oh I agree Brian, lots of them look really cool. I'm partial to the 501st and Shock troopers myself.
But I'm convinced the whole reason for going from white troops to color designations is nothing but marketing for the collectibles side of thing, Hasbro being primary, but others like Gentle Giant and Master Replicas have also benefited. And I've bought right in too, though I think that hunger has been pretty well satiated by now.
But the trooper variations in the OT struck me as functionality chanes to design: snowtroopers with skirts to help keep the extremities warm; biker scouts with more flexible armor for riding the bikes and maneuvering in the bush on Endor. Functionality, not marketing.
In AOTC we met the clones and it seemed that most were white with any variations in color designating rank and not much more. Though I suppose they snuck in the pilots on us, but I'd assumed those were a precusor and functionality thing like the Tie Pilots they resembled. ROTS introduced a spate of different functionality changes in terms of gear and I'm not opposed to that at all. Commanders having different gear than grunts is groovy. Jeez, having different gear for different purposes in different units strikes me as downright logical.
But when I think of the different, blatantly obvious markings on the clones I think marketing, not unit designations. Yeah, you could tell a paratrooper from an SS officer in German militia, but the differences weren't
that obvious. What's the point in the clones on Utapau having orange? I can sort of accept the point of the camouflage on Kashyyk but I'm left scratching my head as a bunch of camo troops are standing on a beach. Huh? Yeah, I know, it was meant more for the forest that seemed to resemble Endor.
I'm just kind of amazed at the inverse evolution of troopers in the Star Wars universe and I'm not sure it's a good thing. I guess my concern stems from a fear of Lucas going back and Ted Turner-ing the OT with troopers from the rainbow world.

It's fun from a toy standpoint and bluntly put it's bloody brilliant marketing considering they can use a half dozen slightly different molds a dozen times each. It's a perpetual money machine. I get it and I'm not against them making money. I just don't think it did anything for the movies is all.