Abstract Geometric Monochrome Pattern Prismatic No Background
Source GDJ
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
From a drawing in 'Jardyne's Wife', Charles Wills, 1891.
Source Firkin
A seamless pattern with green and yellow diagonal lines on top of a white dotted background.
Source V. Hartikainen
Your eyes can trip a bit from looking at this – use it wisely.
Source Michal Chovanec
One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
Background Wall, Art Abstract, Block Well & CC0 texture.
Source Ractapopulous
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Floral patterns will never go out of style, so enjoy this one.
Source Lasma
Fix and cc0 to get the tile this is based on.
Source SliverKnight
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
It’s big, it’s gradient—and it’s square.
Source Brankic1979
Remixed from a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
A free seamless background with pink spots.
Source V. Hartikainen
Not sure if this is related to the Nami you get in Google image search, but hey, it’s nice!
Source Dertig Media
Background formed from the original with an emboss effect.
Source Firkin