A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Prismatic Polka Dots Mark II 2 No Background
Source GDJ
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Remixed from a PNG that was uploaded to Pixabay by VictorianLady
Source Firkin
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 Triangular Seamless Pattern III With Background
Source GDJ
This is a remix of "geometrical pattern 01".
Source Yamachem
Remixed from an image that was uploaded to Pixabay by CatherineClennan
Source Firkin
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
An abstract texture of water. It's not perfect, but will do. You may download if you like it.
Source V. Hartikainen
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Utilising some flowers from Almeidah. To get the unit tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
An attempt for cleaning up the original image in a few steps.
Source Lazur URH
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
Stefan is hard at work, this time with a funky pattern of squares.
Source Stefan Aleksić
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
A very dark spotted twinkle pattern for your twinkle needs.
Source Badhon Ebrahim
If you like it a bit trippy, this wave pattern might be for you.
Source Ian Soper