It's a common trope in Hollywood. Superheroes wearing sparkly tight bodysuits with brilliant colors looks too childish; they have to be BADASS and wear all-black, heavy leather or sythnetic rubber knights' armor. At least they're making Falcon a SHIELD agent, which fits with the black uniform look.
I suspect that this trend was going to be coming to the Avengers characters sooner or later. (The X-Men had already received the black leather Matrix-wannabe treatment.)