I am a flooring contractor and was contacted by a customer to replace prefinished solid 3/4' thick Walnut hardwood due to water damage. The home, in Brentwood, Tennessee was built less than five years ago so thankfully the builder was able to provide the manufacturer and style of the original hardwood. However, I was shocked to see the extreme fading from the original due to the sun and questioned when the hardwood was delivered whether an error had been made. The issue was resolved when the new was compared to the original covered by an area rug. Please view the video which illustrates the affected area.
The photo shows three distinct areas; the new (darkest) medium (under the area rug) and the lightest (exposed to direct sunlight through a french door) And yes, the sunlight caused the extreme fading. The answer...at least be aware that this may happen or provide window coverings or window film so it doesn't happen. And yes, eventually replaced hardwood will fade to match the existing.