The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
Number 4 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Light square grid pattern, great for a “DIY projects” sort of website, maybe?
Source Rafael Almeida
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
The following free background pattern has glossy diagonal stripes as a texture to it, and it's colored in a light blue gray color. This background pattern is suitable for using in web design or any other graphic design projects. This applies to all background patterns here.
Source V. Hartikainen
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. Version with black background.
Source Firkin
A seamless pattern formed from miutopia mug remixes on a tablecloth.
Source Firkin
From a drawing in 'Picturesque New Guinea', J Lindt, 1887.
Source Firkin
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Psychedelic Geometric Background No Black
Source GDJ
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
From a drawing in 'From Snowdon to the Sea. Striking stories of North and South Wales', Marie Trevelyan, 1895.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso