A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
Based on several public domain drawings on Wikimedia Commons. This was formed from a rectangular tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Heavily remixed from a drawing in 'Barbara Leybourne; a story of eighty years ago', Sarah Hamer, 1889.
Source Firkin
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 good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
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
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Kaleidoscope Prismatic Abstract No Background
Source GDJ
A seamless background pattern with a texture of wood planks. This wood background pattern has vertically arranged planks. You may try to rotate it 90°, to see how it will look like when the wood planks are arranged horizontally.
Source V. Hartikainen
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks.
Sometimes you just need the simplest thing.
Source Fabricio