Lead glass tile #2048
 Colorful  CC 0

Mostly just mucked about with the colours and made one of the paths in the lead frame opaque. The glass remains transparent.

Source Firkin

 More Textures
Prismatic Geometric Pattern Background No Black #408
 Noise  CC 0

Prismatic Geometric Pattern Background No Black

Source GDJ

Bright Squares #87
 Light  CC BY-SA 3.0

It’s okay to be square! A nice light gray pattern with random squares.

Source Waseem Dahman

Background pattern 214 (colour 5) #2374
 Green  CC 0

A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.

Source Firkin

Beige Paper #83
 Paper  CC BY-SA 3.0

This was submitted in a beige color, hence the name. Now it’s a gray paper pattern.

Source Konstantin Ivanov

Decorative divider 283 (version 2) #1855
 Dark  CC 0

Remixed from a drawing in 'In an Enchanted Island', William Mallock, 1892.

Source Firkin

Transparent Square Tiles@2X #299
 Grid  CC BY-SA 3.0

The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.

Source Nathan Spady

Micro Carbon #7
 Carbon  CC BY-SA 3.0

Three shades of gray makes this pattern look like a small carbon fiber surface. Great readability even for small fonts.

Source Atle Mo

Fabric 1@2X #10
 Light  CC BY-SA 3.0

Semi-light fabric pattern made out of random pixels in shades of gray.

Source Atle Mo

Background pattern 215 (colour 2) #2370
 Blue  CC 0

A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.

Source Firkin