Microsoft releases National Geographic Antarctica PREMIUM, a new theme pack that contains 12 high-quality 4K wallpapers, the description of which reads as follows:
See icebergs, glaciers, and sea caves from the coldest, driest, and windiest continent in these 12 premium 4k images, free for Windows 10 Themes. These images are to be used as desktop wallpaper only.
After downloading the collection, go to Start > Settings > Personalization > Themes and click on the theme you prefer.
To apply and change to the most appropriate color, based on the current wallpaper, go to Customize > Colors > Automatically select a primary color from the background.