Actually, you CAN color your hair with some junk in it! It is also better not to wash your hair 2 days before you color it. That prevents your hair from getting overly fried and too dry. The natural oils that build up in your hair for 2 days will protect your hair from the color.
I color my hair all the time. Sometimes it is clean, and others, I color it first thing in the morning before washing.
Now, for the red shades, it is best to get the hair wet, this will help to hold the red hue better and it won't fade as quickly, as to the other colors, just follow the box instructions and make sure your hair is not full of hair products, this could cause the color to not be as it should.
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