IF you're talking about the normal (default) Windows 10 desktop background, then I think your "update" caught you up with everyone else.
Microsoft decided that they would make that less attractive in one of the more recent builds by adjusting the colors, tint, hues and saturation.
There is another similar post here
After windows log in screen I get the background screen ( windows supplied ) but it shows as a very light screen and not the regular picture,the picture is visible but not as it was showing before in it's normal coloration. What did I screw up ?
www.windows10forums.com
My advice always is....
IF you're going to use a picture, use one that you like either from you personal collection(s) or from another public resource
OR
Just use a Solid Color.
I'll attach one that I use frequently, I find easier on the eyes yet similar to the original rendered in a darker charcoal gray.
Feel free to use or discard it.
It's zipped so you'll need to extract it before you can right click it and choose Set as desktop background