Detailed but still subtle and quite original. Lovely gray shades.
Source Kim Ruddock
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
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
Derived from a drawing in 'The Murmur of the Shells', Samuel Cowen, 1879.
Source Firkin
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
A light gray background pattern with seamless fabric-like texture and almost unnoticeable stripes.
Source V. Hartikainen
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
The image depicts a seamless pattern of a snow crystal.I referred to a book called ”sekka-zusetsu” or "雪華図説" which means an illustrated explanation about snow crystals.This book was published in 1832 (天保3年) or Edo period.For more about "雪華図説",see here:dl.ndl.go.jp/info:ndljp/pid/2536975
Source Yamachem
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
From a drawing in 'Picturesque New Guinea', J Lindt, 1887.
Source Firkin
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen