A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
That’s what it is, a dark dot. Or sort of carbon looking.
Source Tsvetelin Nikolov
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
The following orange background pattern resembles a honeycomb.
Source V. Hartikainen
Zero CC tileable cork floor, photographed and made by me. CC0
Source Sojan Janso
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
From an image on opengameart.org shared by rubberduck.
Source Firkin
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
A dark gray, sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
This is lovely, just the right amount of subtle noise, lines and textures.
Source Richard Tabor
Could be paper, could be a Polaroid frame – up to you!
Source Chaos
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
It was called Navy Blue, but I made it dark. You know, the way I like it.
Source Ethan Hamilton