Ducati seems to reserve silver for special editions. The first year the M750 was offered in the United States (1997), it was silver. The first year the ST2 was offered in the US (1998 ) it was also silver.
The 900SS FE (Final Edition) was silver, and there was at least one special Superbike that came in silver.
Back in 1997 when I was considering buying my first Ducati, I wouldn't even consider the 750 because I had to have red. Now I really like how the silver M750 looks.