A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
Traced from a drawing in 'Household Stories from the Collection of the Brothers Grimm', Wilhelm Carl Grimm , 1882.
Source Firkin
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Small dots with minor circles spread across to form a nice mosaic.
Source John Burks
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Never out of fashion and so much hotter than the 45º everyone knows, here is a sweet 60º line pattern.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
Zero CC tileable pine bark texture, photographed and made by me. CC0
Source Sojan Janso
Simple gray checkered lines, in light tones.
Source Radosław Rzepecki
The tile this is based on can be retrieved by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
A light gray background pattern with seamless fabric-like texture and almost unnoticeable stripes.
Source V. Hartikainen
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
Might not be super subtle, but quite original in its form.
Source Alex Smith
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Sort of like the back of a wooden board. Light, subtle, and stylish, just the way we like it!
Source Nikolalek