Microsoft has added a new theme pack to the Microsoft Store for Windows 10 users. Titled Stunning Waterfalls PREMIUM, the new theme pack contains 19 high-quality 4K wallpapers, the description of which reads as follows:
Waterfalls cascade over mountains, through forests, and onto beaches from China to Iceland in these 19 premium 4k images, free for Windows 10 Themes.
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.