Not so subtle. These tileable wood patterns are very useful.
Source Elemis
A version without colours blended together to give a different look.
Source Firkin
A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Prismatic Groovy Concentric Background 4 No Black
Source GDJ
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
No relation to the band, but damn it’s subtle!
Source Thomas Myrman
A very dark asfalt pattern based off of a photo taken with my iPhone.
Source Atle Mo
The file was named striped lens, but hey – Translucent Fibres works too.
Source Angelica
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
To get the tile this is formed from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Just what the name says, paper fibers. Always good to have.
Source Heliodor jalba
Remixed from a drawing in 'Paul's Sister', Frances Peard, 1889.
Source Firkin
An alternative colour scheme for the original seamless texture formed from an image on Pixabay.
Source Firkin
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
Remixed from a PNG that was uploaded to Pixabay by VictorianLady
Source Firkin