Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Remixed from a vector adapted from a jpg on Pixabay. The tile this is constructed from can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Greyscale version of a pattern that came out of playing with the 'slinky' plug-in for Paint.net
Source Firkin
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Same classic 45-degree pattern, dark version.
Source Luke McDonald
Zero CC plastic pattern texture, photographed and made by me. CC0 *Note, this texture was on the perfectly smooth surface of a plastic shovel scraper, not sure how to call it. Plz coment if you know what its called.
Source Sojan Janso
The classic notebook paper with horizontal stripes.
Source Are Sundnes
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A white version of the very popular linen pattern.
Source Ant Ekşiler
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. A version of the original with random colors.
Source Firkin
A repeating background of thick textured paper. Actually, it turned out to look like something between a paper and fabric.
Source V. Hartikainen
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim