This is the degree to which the colour is retained under all kinds of conditions such as light, perspiration, rubbing, chloring and washing. The energy of sunlight is so strong that anything exposed to it changes, ages, or oxidises. Just look outside on the facade of a house, when you go to look at the downspouts that are in the sun for part of the day. Then you will see that the colour on the sun side is different from the shaded side. This is because the PVC changes with light. The structure changes, the elasticity decreases, it may oxidise much more and faster. So because of the physical and chemical changes, the colour also changes with it. People used to lay washed white clothes and fabrics on the grass in the sun to dry but also to bleach.

To minimise discolouration in warm and sunny weather, clothes should be washed immediately after a day's wear. This is because sweat contains acids and salts that end up in clothing when worn. When the acids and salts are exposed to the sun the next day, they react chemically with the dyes in the clothes, causing them to discolour. It may be that on the outside the clothes look like they are completely faded but there is nothing on the inside. Some colours like grey and dark green may fade faster than other colours, due to the ingredients in the dye.