Before a full application, check two things: how your hair responds to the colour and how your skin tolerates the product. Indigo-based herbal colour does not behave exactly like standard oxidative dye. It tends to coat and bond around the outer layers of the hair, so the visible result is influenced by your natural base colour, porosity, earlier colouring and the way you combine it with henna.
For a strand test, choose a small hidden section of hair or use shed hair collected from a brush. Apply the prepared powder mixture using the same proportions, timing and method you plan to use on your full head. Rinse, dry and view the strand in natural light. This is particularly important if your hair is very light, bleached, heavily damaged or recently coloured with conventional dye, because the product information specifically notes that results may vary or be less predictable in these cases.
For a skin tolerance check, apply a small amount of the prepared mixture to a discreet area of skin and wait to see whether any discomfort appears before using it on the scalp. If you already know your scalp is sensitive, be extra cautious and avoid applying to irritated or broken skin. If you have ongoing scalp problems or a history of strong reactions to hair colour products, ask a qualified professional before use.