Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Zero CC tileable ground cracked, crackled, texture, made by me.
Source Sojan Janso
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
The image is a remix of "edo pattern-samekomon".I changed the color of dots from black to white and added BG in light-yellow.
Source Yamachem
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
Source Firkin
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
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
Wild Oliva or Oliva Wilde? Darker than the others, sort of a medium dark pattern.
Source Badhon Ebrahim
A classic dark tile for a bit of vintage darkness.
Source Listvetra
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Original seamless pattern with an Inkscape filter.
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
Bright Multicolored Floral Background by Karen Arnold from PDP.
Source GDJ
Zero CC tileable bark texture, photographed and made by me. CC0
Source Sojan Janso