Here’s are some simple background images combining colorful gradients and curved shapes. The images, one with cool and the other with warmer colors, are in 4K 3840×2160 resolution and horizontal 16:9 aspect ratio. They are suitable for use as high-resolution computer wallpapers besides background image for your own digital content. 

The images are in the highest uncompressed .png file quality. I made them using Gimp, so they are not AI generated.