I need to make sage green frosting - has anyone tried the "Avocado" color from Americolor?  Just wondering if it is "sagey" enough

I don't know about that specific color, but if you tested it with a little piece and started light you could try it out before doing the whole batch. Wilton has Juniper or Moss Green that would both work for sage. It just depends on what shade you want to end up with.

The avocado creates a nice sage - you can just keep adding until you get the intensity you like.  And you can always add a tiny bit of black or grey to make it more muted/dirty.  

This owl's body was done in avocado - it was premixed for me at a workshop, I would have liked it a bit darker.

I have also used an Avocado petal dust which I loved the look.