Not so subtle. These tileable wood patterns are very useful.
Source Elemis
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
Here's a quite bright pink background pattern for use on websites. It doesn't look like a real fur, but it definitely resembles one.
Source V. Hartikainen
Oh yes, it happened! A pattern in full color.
Source Atle Mo
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Az Osztrák-Magyar Monarchia irásban és képben', 1885.
Source Firkin
Prismatic Curved Diamond Pattern 4 No Background
Source GDJ
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Abstract Arbitrary Geometric Background derived from an image on Pixabay.
Source GDJ
Sometimes you just need the simplest thing.
Source Fabricio
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless pattern with wide vertical stripes colored in pale yellow.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
Zero CC tileable seed texture, edited by me to be seamless from a Pixabay image. CC0
Source Sojan Janso
ZeroCC tileable wood boards texture, photographed and made by me. CC0
Source Sojan Janso