Use a liberal amount of almond oil all over your skin as this nourishes the skin and prevents the colour from having a dehydrating effect on skin. Protect hair with coconut oil and keep it tied.
Use lots of broad sprectrum sunblock lotion on face, neck , arms and legs( all exposed areas) to prevent tanning and damage due to colour and sun exposure.
After playing with the colours, remember not to use harsh soaps, because soap is alkaline and causes further dryness. Instead, use a mild PH balanced cleansing bodywash.
Due to exposure to sun and colours, the skin becomes dry and flaky and normal soap and water will not be very helpful. It is advisable to use some bath oils to clean the skin like olive oil, castor oil, coconut oil or lavender oil. These are rich in antioxidants and hydrate and nourish the skin. These will also reduce itching and irritation on skin.
Always use a mild shampoo, preferably sulfate free to cleanse the scalp and hair and then nourish with a deep conditioning mask, this will keep the hair soft and prevent hair breakage.
If there is any irritation or allergies on skin or hair, meet a dermatologist at the earliest.