Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Abstract Ellipses Background Grayscale
Source GDJ
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Curved Diamond Pattern No Background
Source GDJ
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
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
From a tile that 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
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
Green Background Pattern
Source V. Hartikainen
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
Classic 45-degree pattern, light version.
Source Luke McDonald
A free black metallic background pattern. Here's a new pattern I made that looks metallic.
Source V. Hartikainen
A seamless pattern recreated from an image on Pixabay. It is reminiscent of parquet flooring and is formed from a square tile, which can be recovered in Inkscape by selecting the ungrouped rectangle and using shift-alt-I together.
Source Firkin
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin