This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Greyscale version of a pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Groovy Concentric Background
Source GDJ
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
Sometimes you just need the simplest thing.
Source Fabricio
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
This tiled background comes in red and consists of tiles that look like gemstones. It is more for blogs or social profiles, I think.
Source V. Hartikainen
Carbon fiber is never out of fashion, so here is one more style for you.
Source Alfred Lee
From a drawing in 'A Rolling Stone. A tale of wrongs and revenge', John Hartley, 1878.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
More bright luxury. This is a bit larger than fancy deboss, and with a bit more noise.
Source Viszt Péter
The starting point for this was drawn on the web site steamcoded.org/PolyskelionMaker.svg
Source Firkin
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
Traced from a drawing in 'Household Stories from the Collection of the Brothers Grimm', Wilhelm Carl Grimm , 1882.
Source Firkin