This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
A dark striped seamless pattern suitable for use as a background on websites.
Source V. Hartikainen
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
A seamless pattern of "sewn stripes" colored in light gray.
Source V. Hartikainen
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
A car pattern?! Can it be subtle? I say yes!
Source Radosław Rzepecki
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A repeating background with seamless texture of stone. There haven't been any stone-like backgrounds for a while, so I have decided to create one more. The rest can be found in the appropriate category.
Source V. Hartikainen
A tile-able background for websites with paper-like texture and a grid pattern layered on top of it.
Source V. Hartikainen
From a drawing in 'Hundert Jahre in Wort und Bild', S. Stefan, 1899.
Source Firkin
Remixed from an image on Pixabay, the original having been uploaded by darkmoon1968.
Source Firkin
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics