If I had a camera and saw a car burning, I'd see if there was something I could do first. If not, I'd take a picture regardless of paint color..
I guess the point of the OP is escaping me as those colors are quite common on cars of those years, so the colors didn't enter my consideration of the picture. The flames and the vintage of the auto's are what struck me.
Also, when the picture was taken is salient. It seems we have far more "silver/grey" cars now than we did back then. It would be difficult to not have colorful cars in a photograph back then.