The original has been presented as black on transparent and stored in the pattern definitions. To retrieve the unit tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ
This one is amazing, truly original. Go use it!
Source Viahorizon
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Dark blue concrete wall with some small dust spots.
Source Atle Mo
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Abstract Ellipses Background Grayscale
Source GDJ
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
From a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Gold Triangular Seamless Pattern No Background
Source GDJ
Background pattern made in "Grunge-Like" style. Available in both SVG and JPG formats. Edit to your needs then click the download button.
Source V. Hartikainen
The image depicts a seamless pattern which was made using stripe-like things including borders.I used OCAL cliparts called "Blue Greek Key With Lines Border" uploaded by "GR8DAN" and "daisy border" uploaded by "johnny_automatic".Thanks.
Source Yamachem
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
More in the paper realm, this time with fibers.
Source Jorge Fuentes
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green