"Should" and "Shall" are entirely different words.
The power of the sun to effect building materials should never be underestimated. Materials shall be effected by the sun in one way or another.
- Even with our efforts to treat glazing with coatings in order to reduce UV transmission there is no total banning (that I have ever heard of) of UV transmission.
- Thus one should always expect that susceptible finishes/furnishings/decor inside a home shall be effected.
Case in point: A few years ago I built a home with high-performance Loewen doors and windows (Low-E and 0.30 SHGC). In the master bedroom there were several mixed-media paintings on the wall.
- Those paintings were always out of direct sunlight and far away from any reflected light off of the hardwood flooring. Yet, within a year there were aspects of those paintings that had changed dramatically in color.
- The hardwood flooring in that particular home was selected, in part, for its resistance to color change (and in particular its ability to resist color change as caused by UV transmittance through glazing.) One cannot see on that flooring any difference between the color of the flooring in direct transmitting sunlight throughout the day, and the color of the flooring adjacent to those areas.
- However, even in an area where no direct sunlight hits the floor, there is a color difference under an interior doormat (for example.) Different species of woods used for hardwood flooring will behave differently over time when in the presence of UV.
It's true that most get darker, but some get lighter (bleach.) Some might get darker then lighter with enough bleaching effect. You can see a description of Color Changes in species by clicking here.
Note that resistance to color change is effected by the finish used on the flooring. Some finishes provide more UV protection than others. From what you wrote, it seems that the dealer told you that the flooring would lighten rather than darken. Again, most woods darken, but not all.
The question of "should" can be substituted with the statement, "Your Hickory Pecan floor SHALL fade to a total blonde color."
I hope that this helps you out a bit. I also hope that despite the color change that your flooring still looks fantastic!
For more information:
Check ourwoodfloorrefinishingQ&A section.