Microsoft has added a new theme pack to the Microsoft Store for Windows 10 users. Titled Ice Crystals PREMIUM, the new theme pack contains 15 high-quality 4K wallpapers, the description of which reads as follows:
Etch your desktop with frosty swirls and elaborate patterns in these 15 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.