Because . . . on this site

http://www.lvstriphistory.com/ie/dunes55.htm

We see the marquee on opening night. Star Vera-Ellen and Robert Lamouret are in Red but not Afro-Americans. Think the colors were just used for "effect." Odd that the marquee did not have letters in other colors - common enough today but maybe back in the 50's and 60's, red and black were the only available colors?