#647499

CSS

:root {
  --misty-harbour: #647499;
  --misty-harbour-rgb: 100 116 153;
  --misty-harbour-oklch: oklch(0.56 0.061 266.3);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(222 21% 50%);
  border-color: oklch(0.56 0.061 266.3);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #647499;
  --color-misty-harbour-50: #eef5ff;
  --color-misty-harbour-100: #dfe8fd;
  --color-misty-harbour-200: #c9d4ef;
  --color-misty-harbour-300: #aab7d7;
  --color-misty-harbour-400: #8e9ec3;
  --color-misty-harbour-500: #7386af;
  --color-misty-harbour-600: #627194;
  --color-misty-harbour-700: #4e5a77;
  --color-misty-harbour-800: #384258;
  --color-misty-harbour-900: #262e3d;
  --color-misty-harbour-950: #151a27;
}

SCSS

$misty-harbour: #647499;
$misty-harbour-rgb: 100, 116, 153;
$misty-harbour-light: mix(#fff, $misty-harbour, 20%);
$misty-harbour-dark: mix(#000, $misty-harbour, 20%);

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