Curing happens unevenly in concrete, with parts of the concrete losing or curing faster than others. This leaves different color or darker patches in it. The good news is the bad news: the sealer wisely applied to your concrete also holds in the moisture for a longer period of time. I suspect that these spots will persist through the winter and even out over time – if not sealed.
Applying sealer now will prolong the different patches and spots from curing out over the next year. You face a choice. Seal your concrete now and prolong, protect and strengthen your concrete. This will retain the spotting for a longer time. Or not seal the concrete, let the spots even out over a year or so and leave the concrete unprotected to allow this to improve. Then seal it later after the finish evens out.
Concrete curing is sometimes art and science when it comes to how Mother Nature facilitates curing when in contact with her earth. Traditional concrete sealers are one of two types: Transparent silicone based sealers for white concrete, and acrylic shiny sealer for exposed aggregate concrete to leave a “wet look”. Nu-Way handles good products for both the white concrete and the wet look acrylic.