1) Delete the fillcolor
2) Add properties:
ENUM/BGTYPE/IMAGEFILE
ENUM/SIZINGTYPE/STRETCH,TILE or TRUESIZE
FILENAME/IMAGEFILE/select your image (must be png)
I did this at Explorer & Shell > Explorer > Control Panel > ControlPanel > ContentPane where I had to use a TILE sizingtype:
Sometimes it works but usually it doesn't and then there's nothing you can do.