A greyish blemish on my eye ball?

Eye discoloration: Discoloration on the white of the eye can from several reasons. If it looks grey, it may actually be just a focal area of scleral thinning. When that happens, the underlying pigmented tissue shows through and gives the white of the eye a greyish color. This can also happen from an embedded foreign body or pigmented lesions of the eye surface. See your eye doctor to determine the cause.

Normal variant: Need more info. How long has it been present? Getting bigger? Any vision changes? Most of the time these are not worrisome. Would need to see it to diagnose.