The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
Prismatic Abstract Line Art Pattern Background
Source GDJ
Utilising a bird from s-light and some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A version without colours blended together to give a different look.
Source Firkin
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-I. A version of the original with random colors.
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
Tiny little flowers growing on your screen. Nice, huh?
Source Themes Tube
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
A pale yellow background pattern with vertical stripes. The stripes are partially faded. I think this background image turned out pretty well, especially those faded stripes.
Source V. Hartikainen
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
A seamless texture of a rough concrete surface.
Source V. Hartikainen
As simple and subtle as it gets. But sometimes that’s just what you want.
Source Designova
Detailed but still subtle and quite original. Lovely gray shades.
Source Kim Ruddock
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Derived from a JPG that was uploaded to Pixabay by ractapopulous
Source Firkin
Prismatic Triangular Background Design Mark II 5
Source GDJ
Subtle scratches on a light gray background.
Source Andrey Ovcharov
Zero CC tileable hard cover cells, skin like, book texture. 4K, Scanned and made by me CC0
Source Sojan Janso
Alternative colour scheme. Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Submitted as a black pattern, I made it light and a few steps more subtle.
Source Andy
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A heavy hitter at 400x400px, but lovely still.
Source Breezi
Neat little photography icon pattern.
Source Hossam Elbialy