My G12Ms have got black covers, how are they different to the Greenback?

Although the standard colour for G12M rear covers was green (‘field green’ it was called originally), G12M and G12H speakers were also made with black, as well as grey, beige and cream rear covers at various times. This was probably due to a shortage of the correct colour plastic to make them from (e.g. late delivery of the raw material). The different colour covers were only a cosmetic change not affecting the acoustic performance of the speakers in any way. Black, grey, cream, beige or green, they’re all ‘Greenbacks’.