Temperature: Will heat be needed to speed up the development time? Is the room warm or cool? Do you need to adjust the application method? When lightening hair, mid length and ends can be applied first before the regrowth application as heat will come from the head. 

Existing colour: How light or dark is the natural depth? How many shades depth are you lightening/adding depth to?

The percentage of white: Has the hair got 10%, 15%, 50%, 100% white hair? Do you need to use a different colouring product? 

The test results: Is the hair suitable for the colour selected? Will the condition be compromised? 

The strength of hydrogen peroxide: How many shades of lift is required? Is white hair coverage needed to achieve an even result?

The porosity of hair: Will you need to use a semi? Is permanent colour or a colour refreshing technique needed?

The length of hair: How much product will you need to mix?

The skin tone: Use and identify the client skin tone to select a colour that is a complimentary tone.