Trucks provide much of the outright color in “ Colors of White Rock .” Rolling metal rectangles in pillarbox red, royal blue and bottle green, they glaringly clash with the dun khaki expanses of the Gobi Desert as they roar down its lonesome highways — the surrounding sands so vast and empty as to make the vehicles look like matchbox cars in long shot. Their route is simple and linear, as they ferry loads of Mongolian coal past the Chinese border; there’s not much possibility of getting lost.