Does Having Greasy Hair Allow Hair Dye To Fade Faster?

It depends on what type of hair coulour you have. If its a semi permanent which fades with each wash and you wash your hair regulary because it does get greasy then yes it will make the colour fade quicker. If its a permanent/highlights it shouldnt make much difference. Have you tried a dry shampoo?

I'm not sure but I would assume so. Because the greece would loosen up the chemicals in the hairdye then your wash your hair and the loose chemicals wash out to.