I found a picture today (but can't now remember which book it was in...!) of an M8(A) when it was first rolled out of the factory and photographed in the street, sporting a number 4 which appears to be black.
But later (colour) pictures suggest that when the cars got to round 2 (?) at Bridgehampton (for example, in the Argentsinger Donohue photo book) show the numbers were blue (as per the McLaren lettering and driver names on the flanks), with a fine line around the edge of the white roundels. For comparison, one image has the Penske M6B and the Chaparral 2G in the same shot, on which I'm pretty certain the numbers were black.
However, a black and white shot of Denny's car (5) at the first round (Road America) shows no line around the roundel. A shot of Bruce's car at Laguna Seca, later in the year, is inconclusive on both colour and the roundel.
Colour images accompanying Pete Lyons's Can Am series in 'Vintage Motorsport' are similarly inconclusive.
I'll have a look for more images when I get a moment.
Edited by 2F-001, 20 May 2020 - 19:57.