Red clothes fade their colour faster when exposed on direct sun light, the reason is as follow.
Sun light has what we call in science Ultraviolet Rays. This ray is capable of breaking chemical bonds, and colours in objects are are hold together by their chemical bonds which gives them the colour when exposed to light.
The amount of light a colour absorb determines the type of colour it will reflect. e.g of this is black colour, black colour absorb all the light rays that touches it that is why it becomes black because it does not reflect any colour, instate it absorb all the colour in the light rays.
while colours light white reflect all the light ray striking on it that is why it becomes white because no colour was absorb instate all the colurs were deflected.
In coloured clothes like red, there are light absorbing colours bodies in the dyes called chromophores which is the molecules that has refused to be absorb during the light reflection, that means what we see as red clothe simply mean all other colour present in the light rays has been absorb except the red colour, which now reflected as red cloth. Therefore the bonds that exist in the red cloth can easily be broken by the ultraviolet ray from the sun, when these happen we now say the colour of the cloth has fade.
This phenomenon which the colour fades is known as photodegradation, where by the main reflector bond has been broken leaving it to fade.
caution: to avoid your Red cloth not fading easily, do not dried it direct under the sunlight.