It is hard to think of anything that will NOT fade in ongoing direct sunlight. Rugs, patio umbrellas, roof tiles, plastic flower pots, garden decorations, bricks, etc., will all eventually lose color due to the strength of the sun rays.
I live in a four season state, but everything I leave outside in direct sunlight eventually fades, or suffers damage from rainstorms, wind or snow. My painted cast iron garden furniture need touch-ups or repainting, as do my heavy steel cellar doors.
I cannot blame the manufacturer---Nature is just more powerful than we can overcome. My recommendation is use the rug in a completely shaded area.