Might not be super subtle, but quite original in its form.
Source Alex Smith
Pattern formed from simple shapes. Black version.
Source Firkin
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo
A seamless textured paper for backgrounds. Colored in pale orange hues.
Source V. Hartikainen
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
A large (588x375px) sand-colored pattern for your ever-growing collection. Shrink at will.
Source Alex Tapein
Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
A floral background formed from numerous clones of flower 117.
Source Firkin
U.S.-based National Fire Protection Association standard fire diamond for flagging risks posed by hazardous materials. The red diamond has a number 0-4 depending on flammability. The blue diamond has a number 0-4 depending on health hazard. The yellow has a number 0-4 depending on reactivity. the white square has a special notice, e.g OX for oxidizer.
Source Firkin
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Sometimes you just need the simplest thing.
Source Fabricio
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs