Hello,

 I am making a fondant covered wedding cake that will have scroll on it.

 Do you recommend to use buttercream for the scroll? If not, what else can I use?

 Also, the scroll is a silver color. How can I get this color?

I would pipe it in grey royal icing and then paint it silver.

Or you could make it in fondant or gumpaste depending on what kind of scrollwork it is, then paint it silver like Maybenot says. You can do it with buttercream but it won't look very silver.