More Textures
Green Fibers #91
 Dark  CC BY-SA 3.0

The green fibers pattern will work very well in grayscale as well.

Source Matteo Di Capua

Prismatic Dots Background 8@2X #516
 Noise  CC 0

Prismatic Dots Background 8

Source GDJ

Retro Circles Background 7 No Black@2X #434
 Unknow  CC 0

Retro Circles Background 7 No Black

Source GDJ

Abstract Arbitrary Geometric Background@2X #498
 Noise  CC 0

Abstract Arbitrary Geometric Background derived from an image on Pixabay.

Source GDJ

Prismatic Polka Dots Mark II No Background@2X #531
 Noise  CC 0

Prismatic Polka Dots Mark II No Background

Source GDJ

Colorful Floral Background 2 #487
 Dark  CC 0

Colorful Floral Background 2

Source GDJ

Batthern #324
 Grid  CC BY-SA 3.0

Sometimes simple really is what you need, and this could fit you well.

Source Factorio.us Collective

Seamless Wood Pattern #889
 Wood  CC BY-SA 3.0

A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.

Source V. Hartikainen

Prismatic Floral Background No Black@2X #476
 Light  CC 0

Prismatic Floral Background No Black

Source GDJ

Soft Circle Scales #113
 Light  CC BY-SA 3.0

Japanese looking fish scale pattern.

Source Ian Soper

Prismatic Polka Dots Mark II 2 No Background@2X #533
 Noise  CC 0

Prismatic Polka Dots Mark II 2 No Background

Source GDJ

Prismatic Abstract Line Art Pattern Background 2@2X #568
 Dark  CC 0

Prismatic Abstract Line Art Pattern Background 2

Source GDJ