Installer told me floors need conditioning and rugs may leave marks due to the sun.
I have them on mine and haven't had any problems yet, there on there for about 2 years now. I installed the floor about 6 months before my wife purchased the rugs
Depend on the wood and finish. Some woods ,like cherry, will darken with the sun. Under the rug will stay light. I never recommend rubber backed rugs on hardwood, never, never. The rubber may discolor the wood forever. Its OK to use a regular area rug, with a cloth back and a rug hold underlay.
Like the others said the wood may color naturally around the rugs due to the sun, but another HUGE concern is the rubber backing on most rubber backed carpets is that they can react with the finish on the wood and ruin the wood. The use of special matts under the rug can be used to prevent this. There are a couple types of these thin anti slip rug matts . You must get the one made for wood flooring. They also allow the wood to breathe. Any questions yo can e mail me through my avatar. GL
