A bit simplified version. Although it could be edited out to be simpler. Anyway, this time the tiling is converted to a pattern fill -which is using clipping for the tile's edges.
Source Lazur URH
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
Prismatic Abstract Background Design
Source GDJ
Prismatic Abstract Geometric Background 4
Source GDJ
A very slick dark rubber grip pattern, sort of like the grip on a camera.
Source Sinisha
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
Prismatic Abstract Background Design No Black
Source GDJ
Washi (和紙?) is a type of paper made in Japan. Here’s the pattern for you!
Source Carolynne
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Derived from a drawing in 'The Murmur of the Shells', Samuel Cowen, 1879.
Source Firkin
This one has rusty dark brown texture.
Source V. Hartikainen
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
Traced from a drawing in 'Household Stories from the Collection of the Brothers Grimm', Wilhelm Carl Grimm , 1882.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A nice one indeed, but I have a feeling we have it already? If you spot a copy, let me know on Twitter.
Source Graphiste
Light gray version of the Binding pattern that looks a bit like fabric.
Source Newbury
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
A tile-able background for websites with paper-like texture and a grid pattern layered on top of it.
Source V. Hartikainen
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin