The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
From an image on opengameart.org shared by rubberduck.
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
A white version of the very popular linen pattern.
Source Ant Ekşiler
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This was formed by distorting an image of a background on Pixabay.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Classic vertical lines, in all its subtlety.
Source Cody L
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
I have no idea what J Boo means by this name, but hey – it’s hot.
Source j Boo
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić