A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
The square tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
A browner version of the original weathered fence texture.
Source Firkin
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868
Source Firkin
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Light gray grunge wall with a nice texture overlay.
Source Adam Anlauf
Might not be super subtle, but quite original in its form.
Source Alex Smith
A fun-looking elastoplast/band-aid pattern. A hint of orange tone in this one.
Source Josh Green
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers
Inspired by a drawing in 'Poems', James Smith, 1881.
Source Firkin
Abstract Ellipses Background Grayscale
Source GDJ