I did this for my newspaper class, February issue. Sadly, it didn't print in color, so I wanted to post this, because I can.
Start out with a piece of clothing which is light-colored. Try white or beige. Avoid blues or greens.
Start out with your first color and begin to tint your look.
Use my spray paint tutorial to make the right colors.
Mix your two main colors first.
Next, mix your second color with your first one in a third spray bottle.
Mine came out a lovely lavendar.
I sprayed it around the edges so that it looked like the blue was blending into the red.