Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
You could get a bit dizzy from this one, but it might come in handy.
Source Dertig Media
A seamless pattern created from a square tile. To get the tile, select the pattern in Inkscape and use shift+alt+i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Might not be super subtle, but quite original in its form.
Source Alex Smith
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
Light gray pattern with an almost wall tile-like appearance.
Source Markus Tinner
Plywood Web Background background image for use in web design.
Source V. Hartikainen
Prismatic Geometric Pattern Background
Source GDJ
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
Zero CC tillable hard cover red book with X shape marks. Scanned and made by me.
Source Sojan Janso
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Abstract Stars Geometric Pattern Prismatic No Background
Source GDJ