Take henna powder, around 4-5 tbsp if you want to apply it only around the area which has gray hair and more if you want to apply to your entire scalp. Make a thin paste of henna powder by adding juice of lemon, a tbsp of curd, a tsp of coffee powder (optional), the water of tea leaves and amla mixture which you prepared earlier. Add ½ tsp of mustard oil in this mixture to avoid dryness. Leave this mixture in an iron vessel for about 2 hours. During winter season you add a finely grounded paste of 2 cloves to elude cold. Apply the mixture on the hair carefully, cover gray hair completely. Leave this on for about 3-4 hours. (Some prefer to keep it overnight.) Then rinse off with water.
Mix coffee powder in the water and make a paste of henna with the water. Beat the egg yolk and mix this into henna. Also add brandy to it. Apply the paste and leave it on for 3-4 hours before washing it with lukewarm water.
If your goal is to cover grey hairs, try making a mixture of rosemary and sage. Mix the ingredients in water and allow them to simmer for about a half hour. Once it has simmered, remove the pan from the heat and allow the mixture to steep for a few hours. Apply to the hair and let it dry completely. Then wash and rinse your hair with your normal shampoo. When it has dried, you will see the results. If you want the hair darker, make another mixture and repeat the process.
Take 3 parts of litharge and 2 of quicklime, mix thoroughly; keep in a well stopped bottle. When used mix with water or milk, apply to the hair, and envelope in an oil-skin cap fur 5 or 6 hours.
The only things I can think of are peroxide and bleach for blonde, but both are not so good for your hair. Beet juice tends to stain your hands, but it would probably make your hair purple and come out the next time you wash it.