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

 More Textures
Prismatic Geometric Tessellation Pattern No Background@2X #552
 Noise  CC 0

Prismatic Geometric Tessellation Pattern No Background

Source GDJ

Prismatic Curved Diamond Pattern 2 No Background@2X #539
 Diamond  CC 0

Prismatic Curved Diamond Pattern 2 No Background

Source GDJ

Patern dots #241
 Dark  CC 0

Pattern repeating background 48x48

Source Keistutis

Prismatic Floral Background@2X #474
 Dark  CC 0

Prismatic Floral Background

Source GDJ

Old Mathematics@2X #44
 Stripes  CC BY-SA 3.0

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

Source Josh Green

Greek key pattern 5 #2294
 Dark  CC 0

Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.

Source Firkin

Abstract Ellipses Background #275
 Dark  CC 0

Abstract Ellipses Background

Source GDJ

Faded Yellow Stripes, Background Pattern #1218
 Yellow  CC BY-SA 3.0

A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.

Source V. Hartikainen

Fabric pattern 2 #2396
 Fabric  CC 0

Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.

Source Firkin

Square ornament 38 #2147
 Dark  CC 0

From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.

Source Firkin

Background pattern 223 (colour 3) #2351
 Green  CC 0

Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift-alt-i.

Source Firkin

Retro Squares Background 9 #399
 Dark  CC 0

Retro Squares Background 9

Source GDJ