Not so subtle. These tileable wood patterns are very useful.
Source Elemis
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Prismatic Geometric Pattern Background 2
Source GDJ
A light gray wall or floor (you decide) of concrete.
Source Atle Mo
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The original has been presented as black on transparent and stored in the pattern definitions. To retrieve the unit tile select the rectangle in Inkscape and use shift+alt+i
Source Firkin
Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
Formed from a tile based on a drawing from 'Viaggi d'un artista nell'America Meridionale', Guido Boggiani, 1895.
Source Firkin
A subtle shadowed checkered pattern. Increase the lightness for even more subtle sexiness.
Source Josh Green
These dots are already worn for you, so you don’t have to.
Source Matt McDaniel
He influenced us all. “Don’t be sad because it’s over. Smile because it happened.”
Source Atle Mo
A free pink background pattern.
Source V. Hartikainen
Here's a camo print with more tan and less green, such as might be used in a desert scenario. This is tileable, so it can be used as a wallpaper or background.
Source Eady
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
Prismatic Hypnotic Pattern 2 No Background
Source GDJ
Prismatic Geometric Pattern Background No Black
Source GDJ
Oh yes, it happened! A pattern in full color.
Source Atle Mo
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
Same as Silver Scales, but in black. Turn your site into a dragon with this great scale pattern.
Source Alex Parker