There are many carbon patterns, but this one is tiny.
Source Designova
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
The tile can be had by using shift+alt+i on the selected rectangle in Inkscape
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
Dark blue concrete wall with some small dust spots.
Source Atle Mo
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 an image that was uploaded to Pixabay by starchim01
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
This background pattern contains a texture of yellow wood planks. I think it looks quite original.
Source V. Hartikainen
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
You may use it as is, or modify it as you like.
Source V. Hartikainen
I took the liberty of using Dmitry’s pattern and made a version without perforation.
Source Atle Mo
Alternative colour scheme for the original floral pattern.
Source Firkin