We do have expert "identifiers" on the forum, but I am not one of them! Nevertheless, I will give it a shot.

It looks like something organic to me. Either phytoplankton (plants) or zooplankton (animals). Can you grab two bottles of material at the same time, and put one in your house that only gets some indirect sunlight and put the other in a very dark closet or cabinet? If it is phytoplankton, it should die in a few days in the bottle deprived of light.

Another option (as you say) is just some windblown pollen. It may have been yellowish when it blew in, but is now oxidizing to a brown color or may even be creating a coating of periphyton.

All of the processes I described above are 100% natural and expected in a pond. If you started with a municipal pool filled with chlorinated water as your drinking water supply, it would still develop algae after the chlorine content declined sufficiently.

In my (non-expert) opinion, none of that constitutes a problem, other than it might affect the taste of your water a few weeks of the year.

However, there is actually one dangerous scenario you do need to study. Cyanobacteria algae growing in your pond can create toxicity in your drinking water, or even to pets or livestock using the pond.

If you suspect cyanobacteria, I do NOT know if you can test for that yourself, or need to send it to a lab. Hopefully, some of our actual experts will drop into your thread.

Congrats on your new pond! Water clarity going from 7' to 18" is fairly normal once the water warms and the sunlight increases - stimulating the living organisms in your pond.