Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
A dark background pattern/texture of a dimpled metal plate.
Source V. Hartikainen
This is a hot one. Small, sharp and unique.
Source GraphicsWall
From a drawing in 'Handbook of the excursions proposed to be made by the Lincoln Diocesan Architectural Society, on the 27th and 28th of May, 1857', Edward Trollope, 1857.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
No idea what Nistri means, but it’s a crisp little pattern nonetheless.
Source Markus Reiter
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman
Prismatic Groovy Concentric Background 2
Source GDJ
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
A topographic map like this has actually been requested a few times, so here you go!
Source Sam Feyaerts
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
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
Sounds French. Some 3D square diagonals, that’s all you need to know.
Source Graphiste
Luxury pattern, looking like it came right out of Paris.
Source Daniel Beaton
Detailed but still subtle and quite original. Lovely gray shades.
Source Kim Ruddock
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
A seamless pattern created from a square tile. To get the tile, select the pattern in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom