A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
This is the remix of an OCAL clipart called "Art Nouveau ornament" uploaded by "microcosme".Thanks.This is a seamless pattern of an Art Nouveau ornament.
Source Yamachem
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
This is a grid, only it’s noisy. You know. Reminds you of those printed grids you draw on.
Source Vectorpile
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
Black version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
More in the paper realm, this time with fibers.
Source Jorge Fuentes
This is the remix of "blue wave-seigaiha".The image depicts a seamless pattern of the front upper part of Japanese five yen coin which is used currently.This design represents a rice with ripe golden ears.
Source Yamachem
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
Luxury pattern, looking like it came right out of Paris.
Source Daniel Beaton
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
Prismatic Polka Dots Mark II No Background
Source GDJ
Just the symbols of the signs of the zodiac distributed in a chequer board-like pattern
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
I scanned a paper coffee cup. You know, in case you need it.
Source Atle Mo
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
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.
Source Firkin
A seamless light gray paper texture with horizontal double lines.
Source V. Hartikainen