Traditional Indian henna is great, the hair actually improves in texture and becomes thicker, unlike with chemical colours which ultimately ruin the mane. Buy only pure mehendi-quality henna, not a commercial mix. Use an iron kadai to prepare henna and traditional recipes (tea extract – for a darker tinge, and lime – for conditioning).
If you have never coloured your hair, you are an ideal candidate for henna. (The collective wisdom says that it’s not a good idea to apply henna after you have used chemicals on your hair, or vise versa, unless you want to get ready for a Halloween party.)