"Dark Brick Wall", Background Pattern #1024
 Stone  CC BY-SA 3.0

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

 More Textures
Prismatic Abstract Geometric Background 4 No Black@2X #442
 Dark  CC 0

Prismatic Abstract Geometric Background 4 No Black

Source GDJ

Orange Striped Background Pattern #909
 Stripes  CC BY-SA 3.0

An orange vertically striped background pattern. Feel free to download and use this orange background pattern, for example, on the web). It resembles a wallpaper with vertical stripes or something similar to it.

Source V. Hartikainen

Prismatic Abstract Geometric Background 5 No Black #402
 Noise  CC 0

Prismatic Abstract Geometric Background 5 No Black

Source GDJ

Background pattern 3 #222
 Noise  CC 0

A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.

Source Firkin

Retro Squares Background 5 #395
 Dark  CC 0

Retro Squares Background 5

Source GDJ

Green Fibers #91
 Dark  CC BY-SA 3.0

The green fibers pattern will work very well in grayscale as well.

Source Matteo Di Capua

Subtle Freckles #89
 Light  CC BY-SA 3.0

This is so subtle: We’re talking 1% opacity. Get your squint on!

Source Atle Mo