Micro Carbon #7
 Carbon  CC BY-SA 3.0

Three shades of gray makes this pattern look like a small carbon fiber surface. Great readability even for small fonts.

Source Atle Mo

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Batthern #324
 Grid  CC BY-SA 3.0

Sometimes simple really is what you need, and this could fit you well.

Source Factorio.us Collective

Background pattern 26 (black) #199
 Dark  CC 0

Pattern formed from simple shapes. Black version.

Source Firkin

Seamless Core Pattern 4 #168
 Dark  CC 0

Seamless Core Pattern 4

Source GDJ

Background pattern 259 (colour 6) #2097
 Blue  CC 0

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

Decorative divider 192 #2503
 Dark  CC 0

From a drawing in 'Worsborough; its historical associations and rural attractions', Joseph Wilkinson, 1879.

Source Firkin

Tessellation 15 (colour 4) #2219
 Green  CC 0

The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.

Source Firkin

Diagonal Noise@2X #182
 Fabric  CC BY-SA 3.0

A simple but elegant classic. Every collection needs one of these.

Source Christopher Burton

Lined Paper #362
 Stripes  CC BY-SA 3.0

The classic notebook paper with horizontal stripes.

Source Are Sundnes

Prismatic Snowflakes Pattern 3 No Background #413
 Light  CC 0

Prismatic Snowflakes Pattern 3 No Background

Source GDJ

Prismatic Abstract Line Art Pattern Background 2@2X #568
 Dark  CC 0

Prismatic Abstract Line Art Pattern Background 2

Source GDJ

Abstract Tiled Background Extended 10 #521
 Noise  CC 0

Abstract Tiled Background Extended 10

Source GDJ

Background pattern 302 (colour 2) #1893
 Dark  CC 0

The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.

Source Firkin

Prismatic Isometric Cube Extra Pattern No Background #405
 Light  CC 0

Prismatic Isometric Cube Extra Pattern No Background

Source GDJ