Retro Squares Background 2 #416
 Noise  CC 0

Retro Squares Background 2

Source GDJ

 More Textures
Background pattern 19 (outline) #204
 Light  CC 0

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

Source Firkin

Background pattern 215 (colour 3) #2369
 Pink  CC 0

A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.

Source Firkin

Dark Circles@2X #307
 Dark  CC BY-SA 3.0

People seem to enjoy dark patterns, so here is one with some circles.

Source Atle Mo

Retro Circles Background 4 No Black #422
 Dark  CC 0

Retro Circles Background 4 No Black

Source GDJ

Tactile Noise #5
 Dark  CC BY-SA 3.0

A heavy dark gray base, some subtle noise and a 45-degree grid makes this look like a pattern with a tactile feel to it.

Source Atle Mo

Background pattern 290 #1932
 Dark  CC 0

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

Source Firkin

Background pattern 104@2X #562
 Dark  CC 0

Background pattern 104

Source Firkin

Black And White Floral Pattern Background Inverse #197
 Dark  CC 0

Black And White Floral Pattern Background from PDP.

Source GDJ

Prismatic Dots Background 3@2X #506
 Noise  CC 0

Prismatic Dots Background 3

Source GDJ

Snowflake pattern remix #156
 Dark  CC 0

The base gradient edited so now more details are rendered.

Source Lazur URH

Background pattern blue #1940
 Blue  CC 0

Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady

Source Firkin

Decorative divider 219 #2231
 Dark  CC 0

Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.

Source Firkin