Might not be super subtle, but quite original in its form.
Source Alex Smith
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
A seamless pattern formed from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Prismatic Triangular Background Design Mark II 5
Source GDJ
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
A green background pattern with warped vertical stripes and a grunge look.
Source V. Hartikainen
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin
Lovely pattern with splattered vintage speckles.
Source David Pomfret
Abstract Tiled Background Extended 10
Source GDJ