Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Background Wall, Art Abstract, Blue Well & CC0 texture.
Source Ractapopulous
Non-seamless pattern drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
Prismatic Abstract Geometric Background 4
Source GDJ
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
A free seamless background image with abstract texture of green "curtain".
Source V. Hartikainen
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 dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen