The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
No, not the band but the pattern. Simple squares in gray tones, of course.
Source Atle Mo
A seamless pattern formed from a sports car on clker.com. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
Actually remixed from a pattern on Pixabay. But then noticed a very similar one on Openclipart.org uploaded by btj51q2.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
One can never have too few rice paper patterns, so here is one more.
Source Atle Mo
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
This could be a hippy vintage wallpaper.
Source Tileable Patterns
Beautiful dark noise pattern with some dust and grunge.
Source Vincent Klaiber
This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Remixed from a JPG that was uploaded to Pixabay by Osckar
Source Firkin
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Colorful Floral Background 3 No Black
Source GDJ