Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Little x’es, noise and all the stuff you like. Dark like a Monday, with a hint of blue.
Source Tom McArdle
Sounds like something from World of Warcraft. Has to be good.
Source Tony Kinard
Prismatic Abstract Background Design No Black
Source GDJ
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
From a drawing in 'Danmarks Riges Historie af J. Steenstrup, Kr. Erslev, A. Heise, V. Mollerup, J. A. Fridericia, E. Holm, A. D. Jørgensen', 1897.
Source Firkin
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
A seamless texture of black leather. I think it will look best when used in headers, footers or sidebars.
Source V. Hartikainen
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
Prepared mostly as a raster in Paint.net and vectorised.
Source Firkin
Used in small doses, this could be a nice subtle pattern. Used on a large surface, it’s dirty!
Source Paul Reulat
Did anyone say The Hoff? This pattern is in no way related to Baywatch.
Source Josh Green
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
You may use it as is, or modify it as you like.
Source V. Hartikainen
A seamless texture of an abstract wall colored in shades of light orange brown.
Source V. Hartikainen
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin