Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
A seamless pattern based on a tile that can be achieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Alternative colour scheme for the original floral pattern.
Source Firkin
Has nothing to do with toast, but it’s nice and subtle.
Source Pippin Lee
Love the style on this one, very fresh. Diagonal diamond pattern. Get it?
Source INS
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
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Prismatic Groovy Concentric Background
Source GDJ
An alternative colour scheme to the original seamless pattern.
Source Firkin
The classic notebook paper with horizontal stripes.
Source Are Sundnes
Feel free to use this seamless background texture as a background on a web site. It's colored in a light pink color and is seamlessly tile-able.
Source V. Hartikainen
A free seamless background texture of "timber wall" (colored in dark brown).
Source V. Hartikainen
Vector version of a JPG that was uploaded to Pixabay by theasad121
Source Firkin
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
Might not be super subtle, but quite original in its form.
Source Alex Smith
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
Seamless SVG vector and JPG backgrounds with faded diagonal stripes. The colors are editable.
Source V. Hartikainen