Using heat is a way to accelerate the processing time of hair color, which is why so many salons are equipped with hood dryers. By carefully watching your hair yourself, or having someone else help you, you can easily process your hair and end up with professional, beautiful color.
Apply your hair color or bleach as directed by the at-home kit.
Read the box your hair color or bleach came in to find out the typical processing time. Use this as your starting point. Heat will cut this time nearly in half.
Set a timer for two to three minutes. You will want to check your hair at brief intervals to make sure that the color is processing correctly and to avoid over-processing.
Turn on your hair dryer or hood dryer. If you are using a hood dryer, make sure your head is centered beneath it. If you are using a hair dryer, turn it to the heat setting and move it around your head so that the heat output is evenly distributed to all the hair being colored or bleached.
Turn off the heat and check your hair when the timer goes off. Examine the color closely; you will be able to see the difference already.
Continue alternating between the dryer and the mirror, checking your hair until the color or bleach has been processed to your desired shade.