On page 265 of "60 Years of Chevrolet" by George H. Dammann is a picture of a 1965 C10 with black lettering on a chrome grill and a picture of a panel with a with an all white grill and no black lettering. Looking through the different years, the pattern seems to be that the black lettering was reserved for the Deluxe optioned trucks with chrome trim and bumpers.
