The banners created in previous versions have a dark rendering in 1.15

Hi, In my creative world, I've created a cool banner. However, when I updated Minecraft, the banner are totally different. I made some test and I can confirm that issue only appear in 1.15.1 (The bug still happen on 1.15.2 pre-release 1).

Also, when I want to create a new banner and that I want select a new pattern, the same bug happen, the banner are too dark.

Thanks you!