The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Use shift+alt+i on the selected rectangle in Inkscape to get the tile this is based on
Source Firkin
Prismatic Geometric Pattern Background No Black
Source GDJ
Drawn in Paint.net using the kaleidoscope plug-in and vectorised.
Source Firkin
Horizontal and vertical lines on a light gray background.
Source Adam Anlauf
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Prismatic Groovy Concentric Background 5
Source GDJ
The basic shapes never get old. Simple triangle pattern.
Source Atle Mo
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod
This one could be the shirt of a golf player. Angled lines in different thicknesses.
Source Olivier Pineda
From a drawing in 'Jardyne's Wife', Charles Wills, 1891.
Source Firkin
To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i
Source Firkin
This is the remix of "Colorful Floral Pattern Background 3" uploaded by "GDJ". Thanks.
Source Yamachem
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A seamless pattern formed from a modified version of rwwgub's tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
CC0 and seamless wellington boot pattern.
Source SliverKnight
Prismatic Groovy Concentric Background
Source GDJ
Prismatic Abstract Background Design No Black
Source GDJ
Element of beach pattern with background.
Source Rones
Prismatic Groovy Concentric Background 4
Source GDJ
This light background pattern has a texture of "frozen" surface with diagonal stripes. Here's an yet another addition to the collection of free website backgrounds.
Source V. Hartikainen