Since most of the movie takes place in a drab and colorless funeral home, we need to wake up and pay attention when color appears. A couple of instances worth mentioning:

As Eddie's driving away from the heist, talking on the phone about how the cops were waiting for them at the jewelry store, an orange balloon is briefly seen bouncing behind his car. Tarantino's usually too complicated for this kind of symbolism, and maybe the balloon isn't so much a symbol as a hint. Anyway, it's how we first get the suggestion that the rat is Mr. Orange.

Something pretty similar is visible in the funeral home when White and Pink are in the tiled room wondering about who the rat could be. There are a bunch of jars on the shelf; some of them are pink and white, others orange. The pink and white jars are placed together on the shelf and the orange ones are far away. More foreshadowing.

When Joe gives the crooks their names, it's all random; the names don't seem to mean anything. However, it turns out it's a good way to convey some visual hints about what's going on.