The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Seamless SVG vector and JPG backgrounds with faded diagonal stripes. The colors are editable.
Source V. Hartikainen
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
The classic 45-degree diagonal line pattern, done right.
Source Jorick van Hees
Inspired by a drawing in 'Poems', James Smith, 1881.
Source Firkin
Retro Circles Background 7 No Black
Source GDJ
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
I’m not going to lie – if you submit something with the words Norwegian and Rose in it, it’s likely I’ll publish it.
Source Fredrik Scheide