This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
Remixed from a drawing in 'Works. Popular edition', John Ruskin, 1886.
Source Firkin
Prismatic Groovy Concentric Background No Black
Source GDJ
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
A free tileable background colored in off-white (antique white) color.
Source V. Hartikainen
Geometric lines are always hot, and this pattern is no exception.
Source Listvetra
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
You can never get enough of these tiny pixel patterns with sharp lines.
Source Designova
This light background pattern has a texture of "frozen" surface with diagonal stripes. Here's an yet another addition to the collection of free website backgrounds.
Source V. Hartikainen
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Alternative colour scheme. 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
Geometric triangles seem to be quite hot these days.
Source Pixeden