Red/Black (contains spoilers)
I've seen the movie at least a half-dozen times and the symbolism of color to demonstrate how life is like roulette has become a big sticking point for me.
*Dominos are red and black after the phone call with Manni
*As she flips through who to call for help, there is the sound of a roulette ball spinning
*As she flips through the people alternate red/black backgrounds behind them
*Her room is dark except for a few red articles in her room and one green, so as the camera spins it alternates
*The guy who pops up and says "no more bets"
*Dad's background is black, the same as #20 (may be coincidence). His face is also the 37th to show up (had to watch in .5x speed to find this. That's the same number of slots as there are on a roulette wheel)
*As she run downstairs the dog has a silver collar. The things on a roulette wheel that slow the ball are silver and called "dogs" (thanks tvtropes.org for that one)
*As she runs down the stairs she runs opposite the camera like a ball spinning
*Hands on the clock are red and black (but thats common)
*As she runs the whole movie you'll notice that her background will change between something black and something red with an occasional green. This is especially noticable when she runs through the long brick tunnel. The interior of the brick is black but the exterior is black. As she runs the camera angle shows red/black alternating in the background with the ocassional green tree. This was the one that blew my mind
*Nuns are in black, guy on the bike is in red
*Colors of the three bags? Red, Green, Black.
*Her red hair, green pants, his black vest
*Cops are green? Not sure if this is meaningful or a coincidence
*Dream sequences are half dark, half under red light
Life is sometimes just as random as roulette, and I LOVE that they show it that way.