A few years ago, I got a pair of Hunter rain boots. I don't wear them very often, they're a bit tall for my petite legs and make walking up stairs an inconvenience, but I do like them. When I was putting them on the other day, I noticed that they were turning grey/white. That powdery residue is "bloom" and Hunter makes a spray you can use to turn your matte boots back to the original color. See more about the "bloom" and Hunter care here. The bloom happened more on one boot than the other, and while there's a bit of a glare on the top boot, you can still see the residue on the boot.
I took my spray and followed the directions to clean the boots. After I was done the boots were back to their original black matte and matched better.
While some people may like the look of the bloom, I'm not a huge fan of it turning my black boots grey, so I'm glad they make this spray to clean them.
Have you ever tried out the Hunter Rubber Boot Buffer Spray?
My Hunter Boots (Costco sold them one fall)