This indigo powder is safe for use on all kinds of hair. Indigo can be applied in one step or two step process to get different tones such as Black, Brown, dark brown etc. It gives natural and attractive color to hair without any chemicals. Indigo dispels heat and have a soothing effect and revitalizes the hair. Step 2: Applying Indigo Mix the indigo powder, salt, and cornstarch together and slowly add water to it until you have a thick paste. Divide your hair into sections and apply the indigo paste to it the same way you applied henna. Put on a shower cap and leave it on overnight. Wash off the indigo paste with water and do not use any shampoo or conditioner on it for the next 2-3 days. The black color of your hair may take a couple of days to fully develop.