Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
Submitted in a cream color, but you know how I like it.
Source Devin Holmes
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
The original enhanced with some gradients.
Source Firkin
Prismatic Groovy Concentric Background 2
Source GDJ
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
This reminds me of Game Cube. A nice light 3D cube pattern.
Source Sander Ottens
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Awesome name, great pattern. Who does not love space?
Source Nick Batchelor
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Prismatic Polka Dots Mark II 3 No Background
Source GDJ
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The image is a design of blue glass.How about using it as background image?
Source Yamachem
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
It’s big, it’s gradient—and it’s square.
Source Brankic1979
CC0 remixed from a drawing. Walter Crane, 1914, Firkin.
Source SliverKnight