Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
No relation to the band, but damn it’s subtle!
Source Thomas Myrman
Looks like an old rug or a computer chip.
Source Patutin Sergey
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
A pattern formed from a photograph of a 16th century ceramic tile.
Source Firkin
Remixed from an image that was uploaded to Pixabay by KirstenStar
Source Firkin
All good things come in threes, so I give you the third in my little concrete wall series.
Source Atle Mo
The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.
Source Firkin
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
From a drawing in 'Cowdray: the history of a great English House', Julia Roundell, 1884.
Source Firkin
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
A seamless pattern of "sewn stripes" colored in light gray.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
A repeating graphic with ancient pattern. I came up with this name/title at last minute, so you may find that there is very little of ancientness in this pattern after all.
Source V. Hartikainen
People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
I asked Gjermund if he could make a pattern for us – result!
Source Gjermund Gustavsen
The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
Inspired by a 1930s wallpaper pattern I saw on TV.
Source Firkin
Zero CC tileable hard cover red book, scanned and made by me. CC0
Source Sojan Janso
Number five from the same submitter, makes my job easy.
Source Dima Shiper
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin