One of my favorite techniques is using my Stampin' Up markers to color them. I just ink up any old block with whatever colors suit my fancy.
Then I get them super wet by misting them with water. If I'm working with card stock, I use tons of water, say 10 squirts. If I'm using watercolor paper, I use less water. In this example I was using card stock, so I drenched the block.
Then I stamp it onto a piece of Whisper White card stock. I press down with force to help squish the color around.
Sometimes I let it air dry, but when I'm in a hurry, I use my heat gun to speed up the process! And voila! A stunning bit of background just waiting to be stamped upon.
Tomorrow I'll post some cards that I made using this technique. Give it a try!