Phil is absolutely right on the sand paper.The wet/dry paper grit as you have figured out has left the color. Next one you may want to stay with sand paper that is meant for wood on raw wood. I only use wet/dry paper when working the finish into the wood but never on a light wood that I stain. That’s the way I was trained but never asked why, your experience has broadened my understanding. Kibler has probably seen this before and I’m sure has given good council .