"Please take a floor cleaning product and clean the floor"

I would be sure to use the correct cleaner, absolutely nothing in the way of a any type restorer, polish or an Murphys Oil type product or you may very well ruin it completely.

You have a textured finish. Take a soft plastic nylon brush and scrub, then vacuum the loose particles, then use a toothbrush and scrub and vacuum. The thinner the bristle, the more you will get out.

A new build is supposed to be almost perfect. Don't touch it...call the builder ASAP.

Is it winter where you are, could it be salt from shoes?

try vinegar and water diluted.

As others have mentioned, I would definitely contact the builder. When my husband and I built a few years back, the painters failed to cover our beautiful hardwood floors when they were doing final touch-ups. Needless to say, we had paint splatter (and more) throughout the main floor. (We were livid.) The builder sent a cleaning service out, however, we still had marks embedded in the wood that were still obvious. Your picture reminds me of some of our boards.

Translation please? " would call the builder ASAP like right it at all until it is checked and take pictures now"

call them first and notify them of the issue. if you try doing something to it, they may blame you for the problem and fail to honor any repair.

as was noted,,take lots of pics that show the difference in the pantry.

could be something has gotten trapped in the deeper grain portion of the wood and the joints. is it confined to that one area or is it throughout the floor?

you could try taking a soft, nylon brush or toothbrush, and a very good floor cleaner (NOT murphys or anything w/wax or polish) and see if you can at least clean the joint areas.