A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Number 5 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Might not be super subtle, but quite original in its form.
Source Alex Smith
Fix side and a seamless pattern formed from circles.
Source SliverKnight
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
This is a hot one. Small, sharp and unique.
Source GraphicsWall
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Colour version that is close to the original drawing uploaded to Pixabay by pencilparker.
Source Firkin
A repeating background of beige (or is it more vanilla yellow) textured stripes. One more background with stripes.
Source V. Hartikainen
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Everyone needs some stardust. Sprinkle it on your next project.
Source Atle Mo
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen