Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
No relation to the band, but damn it’s subtle!
Source Thomas Myrman
Pattern produced in Paint.net using the Vibrato plug-in.
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
Psychedelic Geometric Background No Black
Source GDJ
Zero CC tileable dry grass texture, photographed and made by me. CC0
Source Sojan Janso
This is the remix of "Background pattern 115" uploaded by "Firkin".Thanks.
Source Yamachem
The image is a remix of "edo pattern-samekomon".I changed the color of dots from black to white and added BG in light-brown.
Source Yamachem
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A pattern formed from repeated instances of corner decoration 8. To get the basic tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
A white version of the very popular linen pattern.
Source Ant Ekşiler
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
This background pattern contains a texture of yellow wood planks. I think it looks quite original.
Source V. Hartikainen
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein