one more thought. So you don't screw yourself. Go with small quantities for test. Start with 20 part yellow 1 part blue. You can use dropper if paint is not to thick. So it would be 20 drops of yellow 1 drop of blue. Then just add +1 or maybe +5 drops of yellow to the mix, until you see that you are getting close. After that add just +1 drop of yellow. When you figure out your formula for that color write it down somewhere and you are good forever.