The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
U.S.-based National Fire Protection Association standard fire diamond for flagging risks posed by hazardous materials. The red diamond has a number 0-4 depending on flammability. The blue diamond has a number 0-4 depending on health hazard. The yellow has a number 0-4 depending on reactivity. the white square has a special notice, e.g OX for oxidizer.
Source Firkin
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
ZeroCC tileable stone texture, edited from pixabay, CC0
Source Sojan Janso
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
A seamless paper background colored in pale yellow.
Source V. Hartikainen
Farmer could be some sort of fabric pattern, with a hint of green.
Source Fabian Schultz
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
White handmade paper pattern with small bumps.
Source Marquis
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
An abstract pale yellow paper-like background with stains colored in yellow and green.
Source V. Hartikainen
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A repeating background of thick textured paper. Actually, it turned out to look like something between a paper and fabric.
Source V. Hartikainen
An abstract web texture of a polished blue stone (or does it look more like ice).
Source V. Hartikainen
The starting point for this was a texture drawn with the 'Radial Colors' plug-in in Paint.net.
Source Firkin