The colors aren't reversed however. The knight in the photo is a different knight from the white pieces. It's the same board, just a different square.
The white knight pic is flipped. The coordinates say the knight is on a8. The letters should be on the bottom and the numbers along the side, but they're the other way around. The only way that happens is if the photo got flipped. My guess is someone thought the knight looked better facing right instead of facing left.
The simplest fix would be to simply get rid of the coordinates in photoshop. And make sure everyone involved knows to never, EVER flip photos of a chessboard.
I don't know anything about designing, but maybe making the background a gradient might help ease the transition between colors?
Yes that totally makes sense. Its probably difficult to see in the images but there is a gradient on the colors to try to blend them into the shirt color. It's a vignette effect going from light to dark. It really shows up well on the actual shirts. We use a DTG printing process that is high resolution so you get clear and crisp images on the printing.