I'm very worried. small areas of myeline (white part of the brain) are grey (mri scan). but they said it is not ms. what can it be?

A short list: A number of disorders can produce MRI white matter abnormalites including lyme disease, neurosarcoidosis, a post viral state called acute disseminated encephalomyelitis, migraine headache, vasculitis and hypertension. This list is not all inclusive, but includes some of the more common entities. You should speak with the doctor that ordered the test, or asked to be referred to a neurologist.