I had one on my 748sp although I'm unsure if it was OE. IMO it was a gimmic because over time the covering degraded and it was a bitch when it got wet. Andy
Had one on the 748 - looked spot on even when it turned brown when bleached by the sun But a bitch in the wet soaked up the water till you sat on it
Had a 748 with a red Alcantara covered seat, and my current 749 has a black Alcantara seat. I think both looked great. Fair weather rider, so can't comment on the wet weather performance.
Not to my knowledge from what I have come across, most seats were black leathercloth apart from the 998 which was Grey certainly in biposto form. Blue was used on the Ben Bostrom replica 998. The 998 Final Edition had a black carbon type seat covering but was again in leathercloth.
MY02 748s had the grey vinyl seat also, they stained easily and wear badly due to the mid grey shade. Easy enough to recover if you can get the right material and have a staple gun. I used a leather seat cover made for the seat off ebay - much better and easy to fit
I had mine covered with dove grey Alcantara 12 or more years ago. Still looks great. I do have a biposto pilot's seat similarly covered & never used - offers?