A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
A nice and simple white rotated tile pattern.
Source Another One
Green Background Pattern
Source V. Hartikainen
A seamless pattern the starting point for which was a 'colour modulo' texture in Paint.net.
Source Firkin
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
A beautiful dark padded pattern, like an old classic sofa.
Source Chris Baldie
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin