Submitted as a black pattern, I made it light and a few steps more subtle.
Prismatic Arrows Background
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Random Binary Background
Metal-Rusty. CC0 License.
Adapted from an image that was uploaded to Pixabay by Anerma.
Remixed from an image that was uploaded to Pixabay by Pixeline
Vertical and horizontal lines form some cubes.
Fix and cc0 to get the tile this is based on.
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Derived from an image on Pixabay from Merio
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Floors-Tiles. CC0 License.
Remixed from a PNG that was uploaded to Pixabay by gingertea
Paper-Wallpaper. CC0 License.
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Seamless Core Pattern 6
Inspired by this, I came up with this pattern. Madness!
Source Atle Mo
Alternative colour scheme.
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
A very dark spotted twinkle pattern for your twinkle needs.
Source Badhon Ebrahim
Paper. CC0 License.
From a drawing in 'The Quiver of Love', Walter Crane, 1876
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.
From a drawing in 'Az Osztrák-Magyar Monarchia irásban és képben', 1885.
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso