These products will not fade under sun during regular use. Products might incur change in color if exposed to outside pollutants. This can be but not limited to: Abrasive cleaning products containing bleach, ammonia etc., pesticides sprinkled or sprayed, months long exposure of snow with air pollutants, animal droppings uncleaned, food and drinks that are not cleaned in a timely manner.
The best way to clean these products are with lots of water, possibly hosing down or wiping with wet cloth. You can use mild soaps to clean persistent stains. Dawn or Windex seems to be working well.