Hi folks,
My boat came with black snap-on window covers made of Phifertex. You can see through the mesh well enough to cruise with them up, but I usually take them off due to spray, etc. I use several of the folding automotive windshield reflectors when anchored. You can not see through them, but I slide them between the outside of the window and the snap on covers for the hottest part of the day, and they work really well.
Once it cools off, I remove them. Depending on which side of the boat is facing the sun, I can position these reflectors as needed. Low tech for sure, but it works.
Cheers, Bill