What are the panels made of? if they are plastic and schffed there is not much that you can do, as moost of the time its gone threw the color. If its black like from your shoes I use a APC and rub gentley. DO not spray directly on the panel. Spray on a towel then rub if that goes not work you can try laquer thinner but try an area that is not seen to see how the reaction to the color is.
Again what are they made of?