Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Remixed from a JPG that was uploaded to Pixabay by theasad121
Source Firkin
A seamless texture of worn out "cardboard".
Source V. Hartikainen
Drawn in Paint.net and vectorised in Vector Magic.
Source Firkin
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
Beautiful dark noise pattern with some dust and grunge.
Source Vincent Klaiber
A seamless paper background colored in pale yellow.
Source V. Hartikainen
A version without colours blended together to give a different look.
Source Firkin
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Zero CC tileable Laminate wood texture, photographed and made by me. CC0
Source Sojan Janso
Number 4 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos