A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamless pattern formed from a tile made from ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a JPG that was uploaded to Pixabay by susanlu4esm
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
From a drawing of the coat of arms of the Ottoman Empire on Wikimedia.
Source Firkin