A comeback for you: the popular Escheresque, now in black.
Source Patten
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
Remixed from a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
Tiny little fibers making a soft and sweet look.
Source Badhon Ebrahim
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua