Hi Olivier, yes the white car is the way to go! According to Paul Parker in "Jaguar at Le Mans" it ran in the top three for most of the race until the 21st hour when the clutch broke

I cannot find where I read the cars were painted red white and blue

maybe I was dreaming it? Impossible to tell from B&W photos but the 15 and 16 cars do look to be different hues. The 16 car appears darker than 15
The three cars were not official works entries rather privately owned with "subtle" factory support. A toe in the water for Jaguar to see if they could be successful with a purpose built car. The fact that number 17 came so close to the podium gave Jaguar the confidence to build the C and D types. So that white XK120 played a very important role in Le Mans history