No wedding in India is complete without this. There are many tips and tricks for making the color appear real red and deep. My time tested formula is: After the mehendi is applied (at night). Let it dry. Dont worry if the flakes keep falling off. Take care not to touch water. Sleep well. Wash your hands in the morning. This works for me.
Some women have used clove oil, sugar syrup and have tried many stunts that work best for them. Ask me how!