snake's eye
Concentric rings, from the janome-gasa — slender umbrellas of bamboo and oiled washi paper. A bold white ring on red or blue looked like the eye of a snake, and snakes were messengers of the gods, so the eye warded off misfortune. The umbrellas went into bridal dowries: protection from whatever's coming, and one roof for a lifetime. The same rings sit inside a sake taster's cup, where the blue and white let you judge the clarity of what you're drinking.
Most people who make one of these go dark: near-black ink on black is the most-used palette on the site, because a wallpaper that recedes leaves your icons legible. It looks nothing like the bright version below — which is rather the point of being able to pick.
Any color, any size.
Free, no account. PNG or SVG.