I was lucky enough to spend summer 1991 in Montreux, working mostly nights and using my spare time to explore the railways and model shops of Lake Geneva. With no prior knowledge of Swiss railways and no internet, I had to make my own (extensively researched, but perhaps slightly over-simplified) conclusions about train formations.
There were four daytime Eurocity train pairs: EC Cisalpin, Lemano and Lutetia which connected with TGVs at Lausanne and terminated at Milan, and EC Monteverdi which terminated at Venice. All were operated by RABe ‘Grey Mouse’ units with red coupling covers, or by air-conditioned SBB stock in C1 orange livery, hauled by Re4/4 IVs in Bahn 2000 livery.
The only foreign coaches I remember from four months of intensive train-watching were occasional rakes of FS stock in Rosso Fegato livery, possibly replacing SBB stock on IC services, and the ex-SNCF MC76 coaches (in Corail livery with SBB branding) which had recently been added to loco-hauled Eurocity trains.
Outside the 1989-1993 reign of the Grey Mice, published sources and photographs (and my own observations in 1996) show more foreign stock on international services:
TEE Cisalpin was operated by RAe II four-voltage units from 1961, then with loco-hauled SNCF Mistral 69 stock from May 1974
TEE Lemano was operated by FS 2-car diesel units from 1959, then with loco-hauled FS TEE stock from May 1972, adding FS 2nd class coaches from May 1982
Le Lutetia was operated from 1977 with FS loco-hauled stock, mostly in C1 orange livery.
TGVs came to Lausanne in January 1981, but didn’t get to Brig (as a daily TGV des Neiges) until the winter 1995-6 timetable.
In summer 1996 most international services were operated with SBB Eurocity coaches in two-tone grey, but the EC Monteverdi was FS UIC-Z stock plus a restaurant car.
Then came the Cisalpino saga…