Thank you all for the compliments on my snakes and their pics!
The background I use is blue aquarium stones, available at most pet shops in a wide variety of colors. I purchased a mixture of browns and white stones at the same time, but it didn't show as good a contrast as the blue (my favorite color).
Just for kicks, here is my pair of hypos het lavender. B.C., the male, has the darker background color. K.C., the female, looks almost Miami-ish, and has an "attitude". She strikes at me every time I have to do something with her or her tank. She doesn't even like to have her picture taken.