People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
Greyscale version of a pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
From a drawing in 'An Old Maid's Love. A Dutch tale told in English', Maarten Maartens, 1891.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A hint of orange color, and some crossed and embossed lines.
Source Adam Anlauf
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
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Kaleidoscope Prismatic Abstract No Background
Source GDJ
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
It looks very nice I think.
Source V. Hartikainen