I'm in Linux Mint 14, updated to Xfce 4.10.
Wallpapers are black & white only.
I think that happened after I moved the scrolls for brightness and saturation. After putting them back to zero, no color on the desktop image.
Changing from "image" to "image list" or "none" does not remove the image. But an image can be changed with another: but no colors.
(Now the all-gray philosophy of Xfce and Mint has triumphed... but all the same... I want colors back.)