I cannot tell you exactly what the spots are without seeing the MRI scan
small spots like you describe are common and non-specific, and can be cuased by a variety of conditions such as migraine, high blood pressure, hardening of the arteries, among others. Grey versus bright is just a descriptive term of how they look on the MRI. Generally grey means it has been there a while and bright may mean that the spot is more acute.
It does not sound like you qualify for any diagnosis of MS. It sounds like your neurologist is doing the right thing.