As per directions in the Home Haircolor Kit, mix equal parts color with developer. Apply to roots only.Whatever color you do not mix with developer may be saved for the following month's application. Once you mix color and developer you must use it immediately and it may not be saved if it is mixed. You can combine two colors and add equal parts developer to achieve your own special formula. ALWAYS do a strand test and an allergy test according to the kit direction before applying any new color to your entire head.