What Am I Riddles

Question: What goes black when you buy it, red when you use it, and goes white when you throw it away?

Question: My first doth affliction denote,
which my second is destined to feel.
And my whole is the best antidote,
that affliction to soften and heal.

What am I?

Question: I have four wings, but cannot fly.
I never laugh and never cry;
On the same spot I'm always found, toiling away with a little sound.

What am I?

Question: Light hides me and darkness kills me.

What am I?

Question: I only point in one direction,
but I guide people around the world.

What am I?