Here's a quick background. To start you'll need a background stamp, a piece of smooth white card stock and Versa Mark or black pigment ink.
Next use black embossing powder and heat gun to finish off your background stamp.
Now for my favorite part. Smooshing!! You need dye ink and daubers.
Using your daubers and working in a circular motion you are going to work the ink into the card stock. This is called burnishing. Push down when you are working in the ink but remember to work in little circles. You don't want dauber marks so keep moving.
Spread the colors where you want them. You can go back over each one to darken it. Finish up by using the lightest color all over to blend the inks together. This is what you will end up with. A finished background.
Here's my card.
I still have Christmas cards to finish and this is one that sort of uses the same idea as above. I used the SU Lovely as a tree stamp. Stamped it in parts with Versa mark and embossed in Silver. Then worked 3 shades of blue into the card stock working lightest to darkest from the center.