Can you purchase different color blades for ceiling fans if you like a certain fan but the blades are not the right color?

You can take your blades off, wash them and then paint them yourself.

But, yes, you can buy new ones. They're usually held on with two phillips screws. You should probably take one with you to match up the distance between the screw holes.
They should also be all the same size/weight.

What make/model fan do you have?

Ceiling fan replacement blades- Ceiling Fans N More