Darken (reduce the luminance) of this color.

        Args:
            amount (float) :
                Amount to reduce the luminance by (clamped above zero)

        Returns:
            Color

def darken(self, amount):
        ''' Darken (reduce the luminance) of this color.

        Args:
            amount (float) :
                Amount to reduce the luminance by (clamped above zero)

        Returns:
            Color

        '''
        hsl = self.to_hsl()
        hsl.l = self.clamp(hsl.l - amount)
        return self.from_hsl(hsl)