People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Seamless Green Tile Background
Source V. Hartikainen
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
I asked Gjermund if he could make a pattern for us – result!
Source Gjermund Gustavsen
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
The image is a seamless pattern which is derived from a vine .Consequently, the vine got like dots via vectorization.The original vine is here:jp.pinterest.com/pin/500744052301410188/
Source Yamachem
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
Abstract Ellipses Background Grayscale
Source GDJ
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
A seamless paper background texture colored in pale yellow. This seamless texture is ideal for those who need a yellow background image for their website. The texture resembles paper.
Source V. Hartikainen
We have some linen patterns here, but none that are stressed. Until now.
Source Jordan Pittman
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok