I hope you are all doing well!
Since each box of hair color comes with enough to do a full head of hair, and I only need it for an inch at a time, I've been measuring out just enough for what I need. As long as you don't break the seal (just unscrew instead) or premix all of it, it works great. In my kit each bottle of color and developer is 4 oz, so I know that it's a one-to-one ratio. (Be sure to check yours!)
I bought (red) plastic measuring spoons from Dollar Tree to use exclusively for the hair color. Depending on how much my hair has grown, I use either 1 teaspoon of each or 1 tablespoon of each. I mix them well in a ball jar. You can also buy a box of disposable gloves at Dollar Tree and an empty ketchup/mustard type dispenser if you like from DT or save and thoroughly wash out the dispenser from an old hair color box. Because it's kind of thick, I don't especially like to use the dispenser since it's hard to get into the bottle. Instead, I use a (COLORFAST) makeup-type brush to apply the color for more of a highlighted look most of the time, but that's just me. While you're there, you can also pick up a plastic shower curtain or plastic tablecloth to cover your sink to prevent staining.
Even if it didn't save money, I would like this because I don't have to remember to buy hair coloring whenever I get a hair growth spurt. :-) (Because it's so easy, don't accidentally do it too often and over-process your hair.) It DOES save money, though! I've gotten, on average, 5 applications from each box! Instead of $9 each time, that's $1.80 each time!
I hope that helps someone! Blessings to all of you!
"...for the happy heart, life is a continual feast. Better to have little, with fear for the Lord, than to have great treasure and inner turmoil." Proverbs 15:15b-16 NLT
The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty.--Winston Churchill