Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
From an image on opengameart.org shared by rubberduck.
Source Firkin
A very slick dark rubber grip pattern, sort of like the grip on a camera.
Source Sinisha
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
Kaleidoscope Prismatic Abstract No Background
Source GDJ
I’m starting to think I have a concrete wall fetish.
Source Atle Mo
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Sharp diamond pattern. A small 24x18px tile.
Source Tom Neal
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
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
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
Prismatic Groovy Concentric Background No Black
Source GDJ
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
Sometimes you just need the simplest thing.
Source Fabricio
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin