Using a coating with no colour and expecting it to work well is like using sunglasses with no shading.
In order to protect timber from the effects of sunlight (and ultra violet light in particular), it is necessary to reduce the amount of light reaching the surface. In order to do this, the coating must contain a pigment/colour, which by their very nature will alter the appearance of the timber.
In addition, clear finishes have less protection for themselves from sunlight, and may become brittle, peel and crack, leading to extra work at redecoration.
Sikkens Cetol woodstains offer the ideal compromise between protection and colour, giving long-term protection with an easily maintained coating, along with a translucency which enhances the natural features of the timber.