I have always thought of "salt & pepper carpeting" as referring to two-tone carpet, i.e., Fawn & black, red & black, turquoise & black, etc. That's how I have always heard the term used.
RegnalBob stated: "All 1963 & 1964 Avantis with two tone interiors had salt & pepper carpets, except the Fawn & Elk had Black carpet." (paraphasing a little)
Yes, AFAIK that is the lone exception on '63s, AND that Fawn & Elk w/ black carpet interior was available only with either a Gold or Red exterior.
The upholstery & exterior color combinations available are detailed in the Avanti Color & Upholstery Selector book.
--Dwight