You need to change your ghost storey settings, go into the storey settings dialogue (ctrl + 7) and there should be a place to change the colour that the ghost storey appears as... you might have to click a button to enter the ghost storey settings before you have the option to change the colour, i'm not in front of a computer with ArchiCAD on it, so I cant be 100% sure, but... you should be able to figure it out from there..
HTH,
Dan
edit: just a note, the entire storey will appear as this one colour, if you need the ghost storey to be multiple colours... I'm honestly not sure how to go about doing that..
If you want to have them both printed in colour then you can do that in Plotmaker. Very simple just import one storey on top of the other.
Don't forget to use hotspots in order to adjust their position in PM.