The Flash will be red in Justice League! And real red, not a dark, dark bloody maroon or something. Zack Snyder tweeted a picture of himself and Jason Momoa at Leavesden Studios in England and, hidden in the background, is the Flash costume. See for yourself:

That looks pretty correct to me. It's a very shiny version of the costume, reminiscent of the 90s, but it looks like the lightning belt and the ears are there.

There are other costumes in the picture. One is the Aquaman outfit, which we've seen before. Then there's this guy with a scarf around his mouth. The fact that the dummy is bald does not guarantee the character is:

There's also this concept art. Could this be something from Wonder Woman, which is shooting in the UK right now?

This costume is hard to define. It looks like a generic superhero suit, but if you were to paint it green - and add a logo on front - this could be a Green Lantern costume.

Finally there's this silver outfit. Like that black generic supersuit I'm not certain whether this is the final color or what, but those shoulderpads are fierce.

I'm having a hard time identifying these. What are your guesses?