Lionel Legacy/ MTH Premier and Sun Fading

Answer to this question may solve your original question; are you windows newer and using E-glass that reflects the sun's harmful rays?  If yes, you will probably be OK.  If no, then the answer depends on the material and paints used.  LGB equipment is made for outdoor use, and I don't recall hearing anything about their product fading.  Unfortunately, O scale / gauge stuff is primarily used indoors (except for some track lines where the ties are made ultra-violet resistant), so you might have to check with manufacturer about sunlight issues.

Chuck

I have newer windows and over time the sun has faded books on my shelf.  I would move your trains.  Better safe than sorry

In short, yes the sun will eventually fade the colors.  Low E glass simply helps control heat transfer in the infrared spectrum of light.  The light that fades colors is in the ultraviolet spectrum and passed through windows via direct sunlight.  If your windows are in the shade all the time, it's not an issue.  If you are getting direct light on the trains, then over time it will be an issue.

I was going to start a dissertation on thermo-dynamics  and heat transfer specific to glass, but then caught myself and thought better of it.

I have one window in my train area, and direct sun does come in. I went to Home Depot and purchased window tinting - one for 'privacy' since it's on a ground level and second for protection against possible fading.

The windows in my train room don't get any direct sun, I'm safe.  However, there's no household window glazing that will totally stop the fading, so I'd take measures to protect them.