What food color do I add to white Royal Icing to get an ivory (off white) color? I use Americolor or Wiltons. I can't seem to get the right mix.
Also any suggestions on buttercream icing recipes for cookies. Does this dry hard enough to bag and stack?

They make ivory food colors, are you looking for something to use other than that?

Your best bet with using buttercream is to use Rolled Buttercream, there is a recipe here for it. Let me see if I can get you the link.

Here's the link:

http://www.cakecentral.com/cake_recipe-1603-0-Rolled-Buttercream-Fondant-Alternative.html

RBC can be bagged and stacked. I is quite soft, but it does dry some, but not hard. I bag and stack them all the time. Can't wait to see your next creation!