Background pattern 339 (colour) #1708
 Yellow  CC 0

The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i

Source Firkin

 More Textures
Green Gobbler #85
 Dark  CC BY-SA 3.0

Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.

Source Simon Meek

Prismatic Rounded Squares Grid 4 No Background #491
 Noise  CC 0

Prismatic Rounded Squares Grid 4 No Background

Source GDJ

Background pattern 224 (colour 6) #2337
 Colorful  CC 0

To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.

Source Firkin

Always Grey@2X #54
 Dark  CC BY-SA 3.0

Crossing lines with a subtle emboss effect on a dark background.

Source Stefan Aleksić

Old Mathematics #43
 Stripes  CC BY-SA 3.0

This one takes you back to math class. Classic mathematic board underlay.

Source Josh Green

Prismatic Groovy Concentric Background 3 #457
 Noise  CC 0

Prismatic Groovy Concentric Background 3

Source GDJ

Tessellation 14 variant 1 #2530
 Grid  CC 0

A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.

Source Firkin

Diamond pattern (colour 6) #2280
 Yellow  CC 0

From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Prismatic Hexagonalist Pattern No Background #390
 Light  CC 0

Prismatic Hexagonalist Pattern No Background

Source GDJ

Background pattern 336 (colour 3) #1719
 Blue  CC 0

Formed by distorting the inside front cover of 'Diversæ insectarum volatilium : icones ad vivum accuratissmè depictæ per celeberrimum pictorem', Jacob Hoefnagel, 1630.

Source Firkin

Prismatic Abstract Line Art Pattern Background #565
 Dark  CC 0

Prismatic Abstract Line Art Pattern Background

Source GDJ

Prismatic Rounded Squares Grid 3 No Background #489
 Noise  CC 0

Prismatic Rounded Squares Grid 3 No Background

Source GDJ

Background pattern 227 (colour 4) #2311
 Green  CC 0

A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.

Source Firkin