Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Very dark pattern with some noise and 45-degree lines.
Source Stefan Aleksić
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
A seamless striped fabric-like texture colored in a dark reddish brown color.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
From a drawing in 'Two Women in the Klondike', Mary Hitchcock, 1899.
Source Firkin
A slightly more textured pattern, medium gray. A bit like a potato sack?
Source Bilal Ketab
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
This is a grid, only it’s noisy. You know. Reminds you of those printed grids you draw on.
Source Vectorpile
It’s like Shine Dotted’s sister, only rotated 45 degrees.
Source mediumidee
Carbon fiber is never out of fashion, so here is one more style for you.
Source Alfred Lee
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Prismatic Basic Pattern 2 No Background
Source GDJ
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Everyone needs some stardust. Sprinkle it on your next project.
Source Atle Mo
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Scanned some rice paper and tiled it up for you. Enjoy.
Source Atle Mo