#1570B4

CSS

:root {
  --french-blue: #1570b4;
  --french-blue-rgb: 21 112 180;
  --french-blue-oklch: oklch(0.531 0.133 247.5);
}

.element {
  color: var(--french-blue);
  background-color: hsl(206 79% 39%);
  border-color: oklch(0.531 0.133 247.5);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #1570b4;
  --color-french-blue-50: #d9f9ff;
  --color-french-blue-100: #c7ecff;
  --color-french-blue-200: #a9d9ff;
  --color-french-blue-300: #81bdf9;
  --color-french-blue-400: #58a4e9;
  --color-french-blue-500: #2a8bd9;
  --color-french-blue-600: #2676b7;
  --color-french-blue-700: #1e5e93;
  --color-french-blue-800: #10466d;
  --color-french-blue-900: #0a304d;
  --color-french-blue-950: #001c33;
}

SCSS

$french-blue: #1570b4;
$french-blue-rgb: 21, 112, 180;
$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);
}