Sometimes you just need the simplest thing.
Source Fabricio
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
An abstract web texture of a polished blue stone (or does it look more like ice).
Source V. Hartikainen
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
Prismatic Groovy Concentric Background 2
Source GDJ
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless pattern formed from background pattern 102
Source Firkin
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
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
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten