This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
From a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
As far as fabric patterns goes, this is quite crisp.
Source Heliodor Jalba
This was formed by distorting an image of a background on Pixabay.
Source Firkin
CC0 and seamless wellington boot pattern.
Source SliverKnight
Fake or not, it’s quite luxurious.
Source Factorio.us Collective
Cubes as far as your eyes can see. You know, because they tile.
Source Jan Meeus
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
The following free background pattern has glossy diagonal stripes as a texture to it, and it's colored in a light blue gray color. This background pattern is suitable for using in web design or any other graphic design projects. This applies to all background patterns here.
Source V. Hartikainen
Lovely pattern with splattered vintage speckles.
Source David Pomfret
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.
Source Firkin
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A free seamless texture of reptile skin colored in a dark brown color. As always, you may use it as a repeated background image in your web design works, or for any other purposes.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Snowflakes Pattern No Background
Source GDJ
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Groovy Concentric Background 2
Source GDJ
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Carbon fiber is never out of fashion, so here is one more style for you.
Source Alfred Lee
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
This is sort of fresh, but still feels a bit old school.
Source Martuchox
Inspired by a pattern found in 'A General History of Hampshire, or the County of Southampton, including the Isle of Wight', Bernard Woodwood, 1861
Source Firkin