This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
Zero CC tileable moss or lichen covered stone texture, edited from pixabay. CC0
Source Sojan Janso
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.
Source Atle Mo
Green Web Background, Seamless tile.
Source V. Hartikainen
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Derived from a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Prismatic Geometric Pattern Background 2
Source GDJ
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
A free seamless background texture of "timber wall" (colored in dark brown).
Source V. Hartikainen
Pass parameters to the URL or edit the source code variables to configure the graph paper for the division desired.
Source JayNick
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Seamless Prismatic Quadrilateral Line Art Pattern No Background
Source GDJ