Color fading is a natural phenomenon under the Sun
Due to ultraviolet rays are one of the causes of fading because they can break down chemical bonds and fade the color in an object.Other major contributors to fading include visible light and solar heat. Some objects may be more prone to this bleaching effect, such as dyed textiles and watercolors.
So the Navy blue, dark green, dark red, dark brown and black will appear to fade faster, and they are deeper into the color spectrum than beige, off white, ecru , tan or other lighter colors. It is normal.
If you want use a longer time, we suggest the lighter color.