The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Psychedelic Geometric Background.
Source GDJ
You know I love paper patterns. Here is one from Stephen. Say thank you!
Source Stephen Gilbert
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
Love me some light mesh on a Monday. Sharp.
Source Wilmotte Bastien
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This background pattern contains worn out colorful stripes as a texture.
Source V. Hartikainen
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 bit of scratched up grayness. Always good.
Source Josh Green
Background formed from the original with an emboss effect
Source GDJ
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski
Number 2 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Sharp pixel pattern looking like some sort of fabric.
Source Dmitry
A large (588x375px) sand-colored pattern for your ever-growing collection. Shrink at will.
Source Alex Tapein
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
Remixed from a drawing in 'A Child of the Age', Francis Adams, 1894.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen