This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
Wild Oliva or Oliva Wilde? Darker than the others, sort of a medium dark pattern.
Source Badhon Ebrahim
Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
A heavy hitter at 400x400px, but lovely still.
Source Breezi
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Groovy Concentric Background 5
Source GDJ
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A bit strange this one, but nice at the same time.
Source Diogo Silva
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
The name alone is awesome, but so is this sweet dark pattern.
Source Federica Pelzel
A seamless paper background texture colored in pale yellow. This seamless texture is ideal for those who need a yellow background image for their website. The texture resembles paper.
Source V. Hartikainen