This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Inspired by a drawing in 'Kulturgeschichte', Freidrich Hellwald, 1896.
Source Firkin
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
This one is amazing, truly original. Go use it!
Source Viahorizon
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Dark blue concrete wall with some small dust spots.
Source Atle Mo
An orange vertically striped background pattern. Feel free to download and use this orange background pattern, for example, on the web). It resembles a wallpaper with vertical stripes or something similar to it.
Source V. Hartikainen
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Utilising a bird from s-light and some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
This background pattern contains a texture of yellow wood planks. I think it looks quite original.
Source V. Hartikainen
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
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
The image depicts a Japanese Edo pattern called "kanoko or 鹿の子" meaning "fawn" which has a fur with small white spots.
Source Yamachem