The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
This pattern comes in orange, and it looks as if it is "made of glass".
Source V. Hartikainen
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Dark, lines, noise, tactile. You get the drift.
Source Anatoli Nicolae
Kaleidoscope Prismatic Abstract No Background
Source GDJ
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
Prismatic Groovy Concentric Background
Source GDJ
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
Seamless tile drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
From a drawing in 'Les Chroniqueurs de l'Histoire de France depuis les origines jusqu'au XVIe siècle', Henriette Witt, 1884.
Source Firkin
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Seamless , tileable CC-0 texture. Created by my own, feel free to use wherever you want!
Source Linolafett
Prismatic Groovy Concentric Background 4
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Textured Red Brown Plastic, Free Background Pattern. Although there's already enough plastic in our lives, let's bring it to the web too.)
Source V. Hartikainen