The image depicts a seamless pattern of a snow crystal.I referred to a book called ”sekka-zusetsu” or "雪華図説" which means an illustrated explanation about snow crystals.This book was published in 1832 (天保3年) or Edo period.For more about "雪華図説",see here:dl.ndl.go.jp/info:ndljp/pid/2536975
Source Yamachem
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Prismatic Chevrons Pattern 5 With Background
Source GDJ
This is sort of fresh, but still feels a bit old school.
Source Martuchox
Prismatic Groovy Concentric Background No Black
Source GDJ
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
A classic dark tile for a bit of vintage darkness.
Source Listvetra
This is a seamless pattern which is derived from a flower petal image.
Source Yamachem
This could be a hippy vintage wallpaper.
Source Tileable Patterns
Inspired by a pattern seen on a public domain image of a very old tile. To get the unit cell, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
After 1 comes 2, same but different. You get the idea.
Source Hendrik Lammers
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
This one needs to be used in small areas; you can see it repeat.
Source Luca
Seamless Dark Grunge Texture. Here's a new grunge texture for use as a background.
Source V. Hartikainen