Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
A smooth mid-tone gray, or low contrast if you will, linen pattern.
Source Jordan Pittman
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
Zero CC tillable hard cover red book with X shape marks. Scanned and made by me.
Source Sojan Janso
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Not sure if this is related to the Nami you get in Google image search, but hey, it’s nice!
Source Dertig Media
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
Remixed from a design on Pixabay. To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Looks like an old wall. I guess that’s it then?
Source Viahorizon
This is a remix of "blue wave-seigaiha".I hope this subtle color version of Seigaiha would be suitable for background .
Source Yamachem
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin