What colors to mix to get emerald cake icing?

If you are looking for a causation sort of colour, here's what to do.

I will assume you are working with the standard grocery store liquid colourants.

Start with a very light orange, 1 drop red, 1 drop yellow and mix well. This is most likely going to be way too pale, but as you can add colour but not remove it and you have not given me any idea how big a batch of icing you are working on... better safe than sorry. Next add 1 drop green (yeah, I know, sounds weird, I swear it works), mix well.

Then one drop at a time add red and if needed a bit more yellow. Mix thoroughly after each drop, remember it will dry down a bit darker so keep it pale.

For a darker skin tone use red yellow and blue in equal amounts (1 -2 drops each) to start. Mix well. Adjust by eye with red and yellow until you reach the desired colour.

Remember mix the icing very well after each drop of colour, it is time consuming, but saves you making too many mistakes.