I'm sure that someone out there has asked this question before, but I've had problems in the past with putting ribbon around my buttercream cakes and then noticing that the ribbon soon starts to absorb the "grease" from the buttercream. It turns the ribbon a darker shade and sometimes that interfers with your color coordinating you had in mind.
Anybody else ever have this problem?
Is there a certain ribbon material that will not do this, or should I just live with it!?

Find a plastic-backed velvet ribbon in the same width as the ribbon you want to use. Then, use tiny dots of hot glue, and glue the ribbon you want to be visible to the velvet side of the ribbon.

The grease from the buttercream can't be absorbed through the plastic, so the ribbon you want looks exactly as it is supposed to.

The only issue this really presents is if you are trying to use a sheer ribbon, but it's the best solution I've heard of so far, and I use it every time I use ribbons on cakes.

Hope this helps!

Whenever I use ribbon on a cake, even on fondant, I back the ribbon with scotch tape so when I attach it to the cake, nothing is absorbed through the ribbon. This will work even with clear ribbon. Good luck!