colours.scss

// Map of colours to hex values
$_govuk-colours: (
  purple: #2e358b,
  mauve: #6f72af,
  fuschia: #912b88,
  pink: #d53880
  // etc
);

// Map of deprecated colours and the version in which they will be removed
$_govuk-colours-deprecated: (
  purple: "2.0.0"
);

// Helper function to look-up a colour from the list. Should always use this
// function rather than referencing the map directly.

@function govuk-colour($colour) {
  @if (map-has-key($_govuk-colours-deprecated, $colour)) {
    $version: map-get($_govuk-colours-deprecated, $colour);
    @warn "The colour #{$colour} is deprecated and will be removed in v#{$version}";
  }

  @return map-get($govuk-colours, $colour);
}

.app-button {
  background: govuk-colour(purple);
}