nmctwx wrote:"If it's black, fight back, if it's brown, lay down."
Basically, black bears are less aggressive and dangerous, and typically will leave you alone if you make loud noises (source: in camping with my parents as a kid, we encountered bears a handful of times. With a few odd exceptions, the black bears would run off if you yell at them, but it's till a tense situation.)
Grizzlies, which are always brown, are aggressive, dangerous, and fast. I'm not convinced that playing dead is better than running, but you're not going to scare them off.
The problem with your mnemonic is that "black" bears often look brown. The real difference is in anatomy-- grizzlies have much bigger heads, and thicker necks and shoulders, and when they're on all fours, their heads hang lower than their shoulders. Black bears don't have such obvious shoulder, and narrower, smaller heads.