This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
A seamless paper background colored in pale yellow.
Source V. Hartikainen
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless texture of a rough concrete surface.
Source V. Hartikainen
White little knobs, coming in at 10x10px. Sweet!
Source Amos
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
An emulated “transparent” background pattern, like that of all kinds of computer graphics software.
Source AdamStanislav
This makes me wanna shoot some pool! Sweet green pool table pattern.
Source Caveman
Tiny circle waves, almost like the ocean.
Source Sagive
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
Inspired by the B&O Play, I had to make this pattern.
Source Atle Mo
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
Psychedelic Geometric Background No Black
Source GDJ
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Number 4 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Prismatic Polka Dots Mark II No Background
Source GDJ
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo