Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
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
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
A free pink background pattern.
Source V. Hartikainen
Zero CC tileable brick texture, photographed and made by me. CC0
Source Sojan Janso
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
The act or state of corrugating or of being corrugated, a wrinkle; fold; furrow; ridge.
Source Anna Litvinuk