If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
More in the paper realm, this time with fibers.
Source Jorge Fuentes
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Prismatic Groovy Concentric Background 4
Source GDJ
Zero CC tileable pine bark texture, photographed and made by me. CC0
Source Sojan Janso
CC0 and seamless wellington boot pattern.
Source SliverKnight
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Prismatic Triangular Background Design Mark II 5
Source GDJ
On a large canvas you can see it tiling, but used on smaller areas, it’s beautiful.
Source Paul Phönixweiß
From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin