@rach2jlc is dead on. I love the look and quality Billy Kirk (back before the brand when downhill) leather and canvas brief I own, but have regretted for years buying it in black. I hardly ever wear black clothes or shoes and it generally sticks out because of this.
I love the tone Marvel has established for its cinematic universe. Shoehorning in a dark and brooding tone to some of these characters just wouldn't work. Batman is great for it. Iron Man and Thor? Not so much. It didn't really work all that well for Supernan either.
I don't know. That scene they aired with them all sitting around and trying to lift Thor's hammer had plenty of the trademark humor from the first Avengers. I'm thinking the film won't be as dark as that initial trailer made us believe.