Dash8 DON is right but it goes even deeper (i think)
med gray also varies by country (ie) in the wwii jap navy a med gray was used but it could be one of a doz or more shades that fall within it's spectrum ...each ship yard had its own shade of med gray for the ships either built or refitted at them
then every country's a/f had an doz or more of diif shades they used
and btw the green you were referring to is called zinc chromate...even that varies from a green and goes into shades of yellow
take care
joe