What will give me a aqua blue?
Aqua is one of those subjective colors . I like Wilton Teal as a start - it is readily available and is a very good "Tiffany blue" base. You can add a bit of blue or green to the teal to customize it, depending on the exact aqua you want. Teal and Moss Green are the only Wilton colors I continue to replace as I use them up.