Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
From a drawing in 'Studies for Stories', Jean Ingelow, 1864.
Source Firkin
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
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
This was formed by distorting an image of a background on Pixabay.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
Derived from an image that was uploaded to Pixabay by darkmoon1968
Source Firkin