I remember the first silver and blue paint job I saw -- an R-17 on the 6 pulling into Grand Central on the downtown side. I thought it looked great -- until I stepped inside and saw that gray-and-green paint scheme.
As the 70s wore on, it seemed like the MTA's attitude towards maintenance was "if we paint it, maybe no one will notice half the door leaves are broken and the lights don't work." Combined with the onset of the graffiti scourge, I came to associate the blue-and-silver with the decline of the subway system.