Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
Seamless Background For Websites. It has a texture similar to cork-board.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
ZeroCC tileable mossy (lichen) stone texture, edited from pixabay. CC0
Source Sojan Janso
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
A very dark spotted twinkle pattern for your twinkle needs.
Source Badhon Ebrahim
A seamless textured paper for backgrounds. Colored in pale orange hues.
Source V. Hartikainen
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A seamlessly tile-able grunge background image.
Source V. Hartikainen
Prismatic Curved Diamond Pattern 3 No Background
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
CC0 remixed from a drawing. Walter Crane, 1914, Firkin.
Source SliverKnight
The image a seamless pattern derived from a weed which I can't identify.The original weed image is from here:https://jp.pinterest.com/pin/500744052301423641/
Source Yamachem
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Sounds French. Some 3D square diagonals, that’s all you need to know.
Source Graphiste
Prismatic Groovy Concentric Background No Black
Source GDJ
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Abstract Tiled Background Extended 8
Source GDJ
A background pattern with blue on white vertical stripes.
Source V. Hartikainen
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin