Seamless pattern the basic tile for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Light and tiny, just the way you like it.
Source Rohit Arun Rao
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
A colourful background drawn originally in paint.net and vectorised in Vector Magic.
Source Firkin
Same as the black version, but now in shades of gray. Very subtle and fine grained.
Source Atle Mo
Prismatic Abstract Geometric Background 5
Source GDJ
Prismatic Groovy Concentric Background No Black
Source GDJ
The image depicts a seamless pattern which includes hexagonally-aligned gourds with BG in light-brown.
Source Yamachem
Design drawn in Paint.net, vectorised using Vector Magic and finished in Inkscape.
Source Firkin
Here I have tried to create something that would look like maple wood. Not sure how well it's turned out, but at least it looks like wood.
Source V. Hartikainen
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
A version without colours blended together to give a different look.
Source Firkin
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Super detailed 16×16 tile that forms a beautiful pattern of straws.
Source Pavel