This is really lovely, Lotus! It's stunning!
For fire, I use the dogde and burn tools. Burn tools especially create a darkening look.
Also, I dunno if it's because of just what you wanted it to be (and it looks fine this way, really, the all white is nice), but the mockingjay is also black.

SPOILER ALERT
In the books, Katniss's mockingjay dress is described to have black and white just like the bird. They also mention this again throughout the series, but I can't remember which book. Which is pathetic 'cause I've known the series since 2009. lol