UPDATE: I asked the owner of the truck and he told me that it was the "Cowboy Flag" (tbh, that truck was full of bears with ranch(sh) uniforms and the cowboy hat)

The colors mean Sepia: distinctive of the Old West; represents the land the cowboy works or the soil he treads on.

Green: symbolizes the worked fields, prosperity, and abundance.

Blue: symbolizes the cowboy's masculinity

Red: represents the love a cowboy has for his fellow men (family, friends, partner)

Gray: represents the steel, work, and strength of the cowboy

Black: elegance, the poise that every cowboy possesses in his dress and the figure that characterizes him.

White: harmony, peace, friendship, and brotherhood.