Can you elaborate a bit on this and/or share an image? Not sure I’m seeing what you’re seeing on the NTP.
You haven’t noticed it yet, but once you see it, you can’t unsee it. There is a dark gradient over every image on the new tab page. It affects Brave images and completely ruins custom images—especially the white ones. I’ve already written about it (here: Gradient over new tab images), and it seems I wasn’t the first to notice it (here: A lot of problems with background images on the new tab page).