#066EBE

CSS

:root {
  --french-blue: #066ebe;
  --french-blue-rgb: 6 110 190;
  --french-blue-oklch: oklch(0.531 0.149 250.4);
}

.element {
  color: var(--french-blue);
  background-color: hsl(206 94% 38%);
  border-color: oklch(0.531 0.149 250.4);
}

Tailwind CSS v4

@theme {
  --color-french-blue: #066ebe;
  --color-french-blue-50: #d7f9ff;
  --color-french-blue-100: #c5ecff;
  --color-french-blue-200: #a6d9ff;
  --color-french-blue-300: #7ebcff;
  --color-french-blue-400: #52a3f3;
  --color-french-blue-500: #1f89e4;
  --color-french-blue-600: #1e74c0;
  --color-french-blue-700: #185d9b;
  --color-french-blue-800: #094573;
  --color-french-blue-900: #063051;
  --color-french-blue-950: #001c36;
}

SCSS

$french-blue: #066ebe;
$french-blue-rgb: 6, 110, 190;
$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);
}