The best way is to use an online tool designed specifically for this. I recommend the
Vorici Calculator. It uses the actual attribute-weighted socket color mechanics from Path of Exile to give you:
Exact probability of rolling your desired colors
The average cost in chromatic orbs
Different strategies (like using Vorici’s crafting bench or tainted chromatic orbs)
That way, instead of guessing, you can plan the most efficient route and save a lot of currency.