#657591

CSS

:root {
  --misty-harbour: #657591;
  --misty-harbour-rgb: 101 117 145;
  --misty-harbour-oklch: oklch(0.56 0.048 261.5);
}

.element {
  color: var(--misty-harbour);
  background-color: hsl(218 18% 48%);
  border-color: oklch(0.56 0.048 261.5);
}

Tailwind CSS v4

@theme {
  --color-misty-harbour: #657591;
  --color-misty-harbour-50: #eef5ff;
  --color-misty-harbour-100: #e0e8f8;
  --color-misty-harbour-200: #cad5e9;
  --color-misty-harbour-300: #abb8d1;
  --color-misty-harbour-400: #8f9fbb;
  --color-misty-harbour-500: #7587a6;
  --color-misty-harbour-600: #63728d;
  --color-misty-harbour-700: #4f5b71;
  --color-misty-harbour-800: #394353;
  --color-misty-harbour-900: #272e3a;
  --color-misty-harbour-950: #151b24;
}

SCSS

$misty-harbour: #657591;
$misty-harbour-rgb: 101, 117, 145;
$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);
}