Psychedelic Geometric Background No Black
Source GDJ
Prismatic Snowflakes Pattern No Background
Source GDJ
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by starchim01
Source Firkin
Lovely pattern with some good-looking non-random noise lines.
Source Zucx
It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
A version without colours blended together to give a different look.
Source Firkin