Difficult to say with certainty, but it sure does look like this is due to moisture getting into the flooring. A quick reading using a dual-depth moisture meter would tell you for sure whether or not this is due to the presence of excessive moisture. Also, the blister-type finish blisters you describe would also point towards moisture as being the cause of the darkening.

Thank you. I'll see about testing for moisture. The mystery to me is that one board was black when installed. Coincidence? Or mold already in the board that spread? Hmmmm

Does look like what you would see as darkening from pet urine.

I have kids and a dog that is outside. I have a strong nose, especially when it comes to urine. I would have noticed it :)

The kitchen is on the other side of that wall. There is no sign of water damage on the wall or in the kitchen cabinet.

The dark area has gradually gotten bigger and darker. So gradual that I didn't realize it until I saw the bubble and then looked at the picture from when it was first installed.

Here's a close up pic. You can see the bubble on the top dark board.

Do that test for moisture. If it's way higher in the darkening area than other spots in the room, then moisture is the cause.

Do that test for moisture. If it's way higher in the darkening area, than at other spots in the room, then moisture is the cause.

I'll do that. Thank you.