On a recent trip to House of Edgar, Kelly and I were shown a pattern book from Wilsons (NOT WOB, but another old mill named "Wilsons") from 100 - 150 years ago. The paper was fragile and yellowing. The binding was all but torn apart. The tartans inside were vibrant as the day they were woven. Colors were very similar to the colors used now.

The MAIN factors in how a piece of cloth will wear over time are weather / sunlight / abuse. If the cloth is kept in a safe dry place, it will stay (for the most part) exactly how it was woven for quite a while. If it's worn often and cleaned often (wet washed) and laid out in the sun to dry, it will definitely fade. I've seen kilts from the early 1900's - 1940's where the pleats are faded, but when you open them up, the material underneath is the same color it usede to be.