One week is advised ideally after using Hair Treatment Henna or Cassia Obovata hair treatments. Both treatments have Ayurvedic botanicals that can linger on the shafts of hair for a few days. They continue to nourish and restore the hair during that interval, but may inhibit proper henna-pigment uptake if you try to color too soon. One week and a couple shampoos should be adequate to remove remaining (hard-working) treatment herbs and have freshly prepped hair for color. Note: Amla and Shikakai treatments won't require a week between; best to allow 24 to 48 hours after their use before coloring.