I know it's best to use royal icing when piping on fondant-covered cakes, but is it possible to flood royal icing on a fondant-covered cake w/out it affecting the fondant?
I made a sparky cake (in my photos), that I drew on w/ a food writer pen and then painted in with americolor, but b/c the maroon was so dark, you couldn't see distinct features very well and I thought I might try royal icing next time.
If your fondant has crusted a bit, maybe over night, then using royal flood work will probably turn out just fine. It sounds like a really good idea.
Please post a picture when you get in finished.