I was thinking I'd made scrolls on a wedding cake with modeling chocolate. But after messing around with it, I don't think I can get the chocolate rolled thinly enough to make the look she is wanting. So I guess I'll pipe chocolate buttercream. Will that stick to the fondant and ribbon okay? It's on top of the ribbon. How is a good way to get the buttercream a dark brown?
I am no expert but I have piped buttercream onto fondant and it stayed on fine (see the chocolate heart cake in my gallery). I don't know if it will stick to ribbon or not...what about making chocolate mmf and rolling (or if you have a clay gun, extruding) thin ropes that you can shape into scrolls
As for dark chocolate buttercream...you can use a crusting fudge buttercream recipe I would think.
Piping will stick fine.
Getting a rich brown color:
Add Dutch cocoa powder & brown gel color. I don't measure my cocoa.....just add until I get the color & taste I want. If it get thick - probably will - just add some liquid (can be whipping cream, milk or water as preferred).
You also can actually melt chocolate/dark chocolate and use it for piping too!