#1571B0

CSS

:root {
  --french-blue: #1571b0;
  --french-blue-rgb: 21 113 176;
  --french-blue-oklch: oklch(0.531 0.127 245.5);
}

.element {
  color: var(--french-blue);
  background-color: hsl(204 79% 39%);
  border-color: oklch(0.531 0.127 245.5);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1571b0;
  --color-french-blue-50: #d9f9ff;
  --color-french-blue-100: #c7edff;
  --color-french-blue-200: #a9daff;
  --color-french-blue-300: #81bdf5;
  --color-french-blue-400: #58a5e4;
  --color-french-blue-500: #2a8cd4;
  --color-french-blue-600: #2677b3;
  --color-french-blue-700: #1f5f90;
  --color-french-blue-800: #10466b;
  --color-french-blue-900: #0a314b;
  --color-french-blue-950: #001d31;
}

SCSS

$french-blue: #1571b0;
$french-blue-rgb: 21, 113, 176;
$french-blue-light: mix(#fff, $french-blue, 20%);
$french-blue-dark: mix(#000, $french-blue, 20%);

.element {
  color: $french-blue;
  box-shadow: 0 0 0 2px rgba($french-blue, 0.35);
}