Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Paper model of a tetrahedron. Modelo de papel de um tetraedro.
Source laobc
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Prismatic Abstract Background Design No Black
Source GDJ
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
I’m starting to think I have a concrete wall fetish.
Source Atle Mo
A grayscale fabric pattern with vertical lines of stitch holes.
Source V. Hartikainen
A free background pattern with abstract green tiles.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A free seamless background pattern for use on websites.
Source V. Hartikainen
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
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
Prismatic 3D Isometric Tessellation Pattern 6
Source GDJ
A comeback for you: the popular Escheresque, now in black.
Source Patten
A series of 5 patterns. That’s what the P stands for, if you didn’t guess it.
Source Dima Shiper
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin