Prismatic Abstract Geometric Background 2 No Black
Source GDJ
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
Tile available in Inkscape using shift-alt-i on the selected rectangle
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
Psychedelic Geometric Background No Black
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Here's a subtle marble-like background for use on websites.
Source V. Hartikainen