Max Meyer is believed to have manufactured (most of ) the paints used by Ferrari till mid 60's or so. It is quite clear, however, that color codes were documented for future reference and many Max Meyer codes have an equivivalent in Italver color charts and in some cases (especially during the transition period from MM to Italver) it might be difficult to know who actually manufactured the paint used for a particular car.
As far as I know "MM" was used for Max Meyer, "M" for Metallizato (metallic) and "A" for Acrilico (Acrylic paint).
Best wishes, Kare