You can drag a color or image on to a panel to set the color or image as the background of the panel. You can drag a color or image from many applications. For example, you can drag a color from the file manager to a panel to set the color as the background of the panel. You can also drag a color from any color selector dialog.
You can drag an image to a panel to set the image as the background of the panel. You can also drag pattern images from the file manager to set the background of the panel.