Attached is a source file for making skins.
It was made with a program called GIMP v2.8 which can be downloaded and used for free.
It uses layers like Photoshop or Corel Draw. Simply add a background picture of your choice as a layer, size it to the correct dimensions, and make sure it is the bottom layer so all other layers show on top of it.
Then change the colors of the panels and the color swatches using the paint can tool. Make the colors complement the background using the 'color picker' tool that looks like an eye dropper. It works best to make the secondary color swatch the same as the panel color, then make the primary color swatch a darker or lighter version of the same color.
Then export the file to .bmp, put it in the skins directory, and select it as a skin in Bliss.