This one is something special. I’d call it a flat pattern, too. Very well done, sir!
Source GetDiscount
Spice up your next school project with this icon background.
Source Swetha
Wasn't satisfied with the original's colouring. Too much component transfer and colormatrixes yet the results are lacking a bit. So this time it is a simple black to transparent fade, making it possible remixing easily once there will be other blending modes supported as well. Probably in inkscape 0.92.
Source Lazur URH
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
A gray background pattern with a texture of textile. Suits perfectly for web design.
Source V. Hartikainen
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Prismatic Curved Diamond Pattern 8 No Background
Source GDJ
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
Everyone needs some stardust. Sprinkle it on your next project.
Source Atle Mo
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
A dark metallic background with a pattern of stamped dots. Here's a dark "metallic" background pattern for you.
Source V. Hartikainen
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim