Monochrome color special rule

[silverwind]

I imagine it would be nice to have a special rule that processes monochrome colors and either outputs a pure inversion or a hue-saturation-modified variant.

{
  "$color: $monochrome": "$invert", // pure inversion
  "$color: $monochrome": "$hue(220) $saturate(50)", // shift color to blue
  "$background: $monochrome": "$invert", // pure inversion
  "$background: $monochrome": "$hue(220) $saturate(50)", // shift color to blue
}

If another user rule is present that matches the same value, the user rule should have precedence.