On the Trivia thread @Rollo asked these questions about Eugenio Castellotti:
(1) Is there a reason why 548 had a yellow nose in the Mille Miglia?
(2) How many times did he pair with Fangio?
(3) Is the story of Vittorio Marzotto winning the 1952 Monaco GP true because of a can of Coke true? That just seems a little too fantastic to be true.
(1) This was common practice in both sports car and grand prix racing so that it was possible to distinguish between cars at a distance or at speed. The colours generally had no particular significance.

(2) In grands prix, on two occasions in 1956 (Monaco and Monza) Fangio had taken over Peter Collins' car as his own was giving trouble and Castellotti, who had already retired in his own car, was sent out in the repaired Fangio car to see what place (and prize money) the team could salvage. These will appear in statistics as shared drives.
In sports cars he and Fangio regularly co-drove a car, including
1954 Sebring: Lancia - DNF
1954 Tourist Trophy: Lancia - DNF (both transferred to other cars)
1956 Buenos Aires 1000km: Ferrari - DNF
1956 Sebring: Ferrari - 1st
1956 Nurburgring 1000km: Ferrari - 2nd
1956 Supercortemaggiore race, Monza: Ferrari 500 - 1st
1956 Swedish GP: Ferrari - DNF

(3) It looks as if you got the information from 8W who are generally reliable for facts. However, this particular piece is more of a "magazine article" than a biography. Remember that Coke cans hadn't been invented in 1952 and it's also doubtful whether Coke (in bottles) would have reached Monaco that early. David Hodges' Monaco GP history doesn't mention a stop for a drink. By halfway point all the serious opposition had fallen by the wayside and the two Ferraris had a commanding lead. He and Marzotto then passed and repassed each other several times. Then he says "Both stopped for fuel with 20 laps to go. Castellotti took over a minute, Marzotto 45 sec. That margin decided the race ..."
Draw your own conclusions.
I'll have a look at the Motor Sport report and see if that says anything.