This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
A seamless pattern formed from a square tile based on a jpg on Pixabay. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I.
Source Firkin
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Retro Circles Background 8 No Black
Source GDJ
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo