Background pattern black #2026
 Dark  CC 0

Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

 More Textures
Prismatic Groovy Concentric Background 4 No Black #463
 Noise  CC 0

Prismatic Groovy Concentric Background 4 No Black

Source GDJ

Prismatic Geometric Tessellation Pattern 4 No Background #557
 Noise  CC 0

Prismatic Geometric Tessellation Pattern 4 No Background

Source GDJ

Inflicted #117
 Grid  CC BY-SA 3.0

Dark squares with some virus-looking dots in the grid.

Source Hugo Loning

Background pattern 308 (colour 6) #1867
 Pink  CC 0

Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.

Source Firkin

Rice Paper #338
 Paper  CC BY-SA 3.0

Scanned some rice paper and tiled it up for you. Enjoy.

Source Atle Mo

Prismatic Polyskelion Pattern No Background #394
 Light  CC 0

Prismatic Polyskelion Pattern No Background

Source GDJ

Background pattern 222 #2345
 Green  CC 0

Seamless pattern inspired by a drawing on Pixabay. To get the tile this is formed from, select the rectangle in Inkscape and use shift-alt-i.

Source Firkin

Background pattern 21 #205
 Light  CC 0

A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.

Source Firkin

Seamless Prismatic Quadrilateral Line Art Pattern No Background #379
 Diamond  CC 0

Seamless Prismatic Quadrilateral Line Art Pattern No Background

Source GDJ

MBossed #193
 Grid  CC BY-SA 3.0

Embossed lines and squares with subtle highlights.

Source Alex Parker