The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
One more updated pattern. Not really carbon fiber, but it’s the most popular pattern, so I’ll give you an extra choice.
Source Atle Mo
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
Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile 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
The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
To get the repeating unit, 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
New paper pattern with a slightly organic feel to it, using some thin threads.
Source Atle Mo
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Colour version of the original seamless pattern.
Source Firkin
Actually, there's no clouds in it, but I think it looks quite nice.
Source V. Hartikainen
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
White fabric looking texture with some nice random wave features.
Source Hendrik Lammers