Sitting a chess set close to a bright window will caused fading of kinds , Sun light & wood ,
Just use a microfiber cloth to wipe down , I use cooked linseed oil & give it a good rub down on the board once a year , Works wonders ! This is my rare 60mm SQ from the 50's .
Is it solid wood, e.g. Drueke, Colorado Woodworker, or is it veneer, e.g. rechapados ferrer, sunshine chess?
If solid wood, it’s probably not best to have it constantly exposed to heat/light by a window - and laying flat. The board is likely to warp as well as discolor as you described.
The only way to repair - if you want to repair the discoloration - is to sand it down and refinish *if it is solid wood*. It’s a fairly quick and easy process - less than a week of applying finish (Waterlox satin or Minwax satin polyurethane, 3-5 coats a day apart, wet-sanding in between). Then wait a month and polish + wax.
If veneer, I don’t have the answer (don’t sand!).
Here’s a beat-up old Drueke bought cheap on ebay and refinished this week (December 2024 - will polish & wax mid-January):
Thanks for your input. Just to clarify, the board isn’t in direct sunlight but it is a medium sized bay window around 10ft away.
It’s definitely wood as you can see from the below. It’s not a big problem of course, but hopefully you can see the discolouration.
That looks like a Polish board, but it’s hard to say - for example:
https://www.chesshouse.com/collections/wooden-chess-boards/products/19-wooden-chess-board-without-coordinates?variant=39328525189207
So, wood veneer. They’re good boards and won’t warp. But don’t try to sand them down. I wonder if you left the entire surface exposed, would the tones even put? Anyway, I’d just play on it assuming it doesn’t bother you too much.
I try not to leave my boards out flat and never exposed to direct sunlight. I wax them every couple of years.
Thank you. I wonder if some beeswax polish might help? I could leave the pieces off but I quite like it as a centre piece in the front room.
I don’t know if it will help with the silhouettes, but it won’t hurt the board. Lot’s of info online, e.g.
Does the felt/leather at the bottom of the pieces collect wax? Or does it all stay on the board?
Or is waxing meant for display boards that you don't play constantly?
Does the felt/leather at the bottom of the pieces collect wax? Or does it all stay on the board?
Or is waxing meant for display boards that you don't play constantly?
After waxing or Oiling wood , You should let it seep for at least a day or more pending ? , then buffer with a dry soft rag to take away the excess . Bingo 
My main board is a walnut and ash matt construction that is on display with a large window in close proximity. It’s only a year old and the dark squares that have a piece sat on them have lightened, where those pieces sit. As it’s a matt finish, I’m guessing that it must be waxed occasionally. Does it need a rub down and wax reapplying every now and then?