If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Colour version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
A pattern formed from a photograph of a 16th century ceramic tile.
Source Firkin
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Prismatic Abstract Line Art Pattern Background
Source GDJ
Lovely light gray floral motif with some subtle shades.
Source GraphicsWall
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Light square grid pattern, great for a “DIY projects” sort of website, maybe?
Source Rafael Almeida
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
Tiny little fibers making a soft and sweet look.
Source Badhon Ebrahim
Prismatic Curved Diamond Pattern 8 No Background
Source GDJ
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Old China with a modern twist, take two.
Source Adam Charlts
Derived from a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua