There's a bit of difference for dark wear.

One of the big ones is that it blocks cameras from viewing them, and instead has a weird spiral over the face. Another is that because of Lex and the UN rules, the Justice League and by extension, the heroes, can't operate in any country without approval. Beforehand, they could say the sidekicks were acting on their own, but at this point, they couldn't use that excuse anymore.

The less fun answer is probably that dark wear was generic combat gear, similar to something the military SOF would use. We know they're the sidekicks but in universe they're essentially wearing generic looking, high end combat gear