Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
Abstract Tiled Background Extended 6
Source GDJ
This one takes you back to math class. Classic mathematic board underlay.
Source Josh Green
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868.
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Abstract Geometric Background 4
Source GDJ
Prismatic Groovy Concentric Background 4
Source GDJ