Customize the Volume HUD. Choose from a Color (or use the RGB sliders), Gradient, or a Picture. You can choose both gradient stops from RGB sliders, or choose a random color. You can also completely hide the HUD by dragging the Opacity Slider to 0. In addition, you can choose whether you want to have the gradient horizontal or vertical.
To use a picture, save it as /var/mobile/Library/volumebg.png
It can be a jpeg, or gif, but it must be saved as volumebg.png
PICTURE BACKGROUND IS EXPERIMENTAL AS IT HIDES THE INDICATOR AT THE BOTTOM. Gradient and Color work well, though.
Configure options in the settings app.