Why the Chessboard is checkered?

Since the Q and B move diagonally and the P takes that way, having different colors on adjacent diagonals helps the players see the diagonals better and prevent mistake moves.

As a tournament director in USCF scholastic tournaments I was sometimes called to a table because, after several illegal moves, the players suddenly realized one side had two bishops on the same color, Without a difference in diagonal colors, it wouldn't have been noticed. It helped me reconstruct the last legal position when the teenagers - whose scorecards were often faulty - could remember where a piece was - working backward through each move - and the diagonals sure helped them visualize the layout.