A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Wasn't satisfied with the original's colouring. Too much component transfer and colormatrixes yet the results are lacking a bit. So this time it is a simple black to transparent fade, making it possible remixing easily once there will be other blending modes supported as well. Probably in inkscape 0.92.
Source Lazur URH
Number five from the same submitter, makes my job easy.
Source Dima Shiper
Prismatic Rounded Squares Grid 4 No Background
Source GDJ
Sharp but soft triangles in light shades of gray.
Source Pixeden
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
A bit like smudged paint or some sort of steel, here is scribble light.
Source Tegan Male
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
A simple bump filter made upon request at irc #inkscape at freenode. Made a screen capture of the making here: https://youtu.be/TGAWYKVLxQw
Source Lazur URH
A comeback for you: the popular Escheresque, now in black.
Source Patten
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This seamless light brown background texture resembles a wallpaper with vertical stripes. One way to use it is as a tiled background on web sites.
Source V. Hartikainen
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
Colour version of the original pattern.
Source Firkin
White circles connecting on a light gray background.
Source Mark Collins
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A black tile-able background with paper-like texture.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin