This was formed by distorting an image of a background on Pixabay.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
The starting point for this was drawn on the web site steamcoded.org/PolyskelionMaker.svg
Source Firkin
Prismatic Floral Background No Black
Source GDJ
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. A version of the original with random colors.
Source Firkin
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Prismatic Groovy Concentric Background 5
Source GDJ
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A background pattern with wavy green vertical stripes. This one has green stripes on a white background. Download if you like it.
Source V. Hartikainen
Colorful Floral Background 3 No Black
Source GDJ
A free background tile with a pattern of pink bump dots. This background tile is sweet! Moreover, it's designed for use as website backgrounds.
Source V. Hartikainen
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
More in the paper realm, this time with fibers.
Source Jorge Fuentes
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
From a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
A grayscale fabric pattern with vertical lines of stitch holes.
Source V. Hartikainen
A white version of the very popular linen pattern.
Source Ant Ekşiler