"If it's black, fight back. If it's brown, lie down."
That's shortened to the point of being useless and leaves out the parts that actually matter.
First of all, there are black grizzlies and brown "Black bears" and the sizes of the species overlap. It may be hard to identify a bear that's coming at you.
Here's what you should do: Carry pepper spray whenever you're in bear country!
When you encounter a bear close up, stand still, take out your pepper spray (or anything you can use as a weapon) and start talking to it calmly. Let it know you're a human and neither aggressive nor afraid. Ask it how its day is going.
If it backs down, you walk backwards slowly till it's out of sight, then find a different route.
If it stops, advances or charges, you stand still, facing it. Don't run or climb a tree.
Most charges are mock charges where it'll stop before you.
If it doesn't stop and gets within 20 feet, shoot your pepper spray, which was shown to stop 95% of bear attacks.
In the other 5% fight for your life. Aim for the nose. Good Luck!
Lying down might sometimes be better if it's a Grizzly, depending on its motivation to attack you, but there's no way you can know that. Chances are, after its first slap you're lying down anyway.
Source: worked as a ranger in British Columbia
