Brown hair with 20% gray can use the following formulation: Medium brown will impart lighter highlights where the gray is with warm undertones(reddish) Medium ash brown will make the color a more neutral brown with less red. Dark brown will look medium brown on the grays with warm tones. Dark ash brown will look like dark brown with no warm tones. Golden blonde warm will look blonde on the grays and your brown hair will either be golden brown or quite golden depening on the porosity and the amount of warm undertones in your hair. ALWAYS do a strand test on a small section of hair before applying any new color formulation to your entire head.