what colors do I need to mix to make it tiffany blue

I like just a touch of Wilton's teal, works pretty well.

I've never made it, but if you enter the word tiffany in the forum's search box, you'll see a number of posts that ask and answer this question.

P.S. The bow in my avatar was made using teal, but looked more turquoise than Tiffany blue in real life.

I use equal parts teal and sky blue, with a teensy weensy dot of black. It comes out perfect every time.