The image depicts a seamless pattern of a Japanese family crest called "chidori" in Japanese .A chidori in Japanese means a plover in English.
Source Yamachem
Might not be super subtle, but quite original in its form.
Source Alex Smith
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Prismatic Groovy Concentric Background 5 No Black
Source GDJ
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
Prismatic Abstract Line Art Pattern Background 2
Source GDJ
A re-make of the Gradient Squares pattern.
Source Dimitar Karaytchev
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
Simple combination of stripy squares with their negatively coloured counterparts
Source Firkin
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Remixed from a drawing in 'Line and form", Walter Crane, 1914.
Source Firkin
Inspired by a design found in 'Konstantinápolyi emlékeim', Miklos Chriszto, 1893.
Source Firkin
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin