This one needs to be used in small areas; you can see it repeat.
Source Luca
This light yellow background pattern consists of an irregular pattern of spots. Here's a light background pattern with yellowish tint.
Source V. Hartikainen
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Prismatic Basic Pattern 2 No Background
Source GDJ
Prismatic Snowflakes Pattern No Background
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
From a drawing of the coat of arms of the Ottoman Empire on Wikimedia.
Source Firkin
Prismatic Abstract Geometric Background 4
Source GDJ
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Seamless Prismatic Geometric Pattern With Background
Source GDJ
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Carbon fiber is never out of fashion, so here is one more style for you.
Source Alfred Lee
An interesting dark spotted pattern at an angle.
Source Hendrik Lammers