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
Zero CC Mossy stone tileable texture, photographed and made by me. CC0
Source Sojan Janso
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Derived from a PNG that was uploaded to Pixabay by nutkitten
Source Firkin
Like the name says, light and gray, with some small dots and circles.
Source Brenda Lay
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
A seamless pattern made from the gold Penrose triangle by GDJ and the two remixes
Source Firkin
Just like your old suit, all striped and smooth.
Source Alex Berkowitz
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Very simple, very blu(e). Subtle and nice.
Source Seb Jachec
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
A lovely light gray pattern with stripes and a dash of noise.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin