A light gray wall or floor (you decide) of concrete.
Source Atle Mo
The tile this fill pattern is based on can be had by using shift+alt+i on the rectangle.
Source Firkin
Background formed from the original with an emboss effect
Source GDJ
Prismatic Rounded Squares Grid 3 No Background
Source GDJ
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
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
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Colour version of the original seamless pattern.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
White circles connecting on a light gray background.
Source Mark Collins
Prismatic 3D Isometric Tessellation Pattern 6
Source GDJ
Remixed from an image that was uploaded to Pixabay by KirstenStar
Source Firkin
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
Imagine you zoomed in 1000X on some fabric. But then it turned out to be a skeleton!
Source Angelica
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Abstract Ellipses Background Grayscale
Source GDJ
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Formed by heavily distorting part of a an image of a fish uploaded to Pixabay by GLady
Source Firkin
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom