Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
Inspired by a 1930s wallpaper pattern I saw on TV.
Source Firkin
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
A light gray fabric pattern with faded vertical stripes.
Source V. Hartikainen
A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
This was formed by distorting an image of a background on Pixabay.
Source Firkin
White circles connecting on a light gray background.
Source Mark Collins
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
It’s okay to be square! A nice light gray pattern with random squares.
Source Waseem Dahman
A seamless pattern made from the gold Penrose triangle by GDJ and the two remixes
Source Firkin
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
A repeating background with dark brown stone-like texture and abstract pattern that looks like tree trunks.
Source V. Hartikainen
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin