def validate_value(value)
      unless value.is_a?(String)
        raise TypeError, "can't convert #{ value.class } into PryTheme::HEX"
      end
      if value !~ PryTheme::HEX::PATTERN
        fail ArgumentError, %|invalid value for PryTheme::HEX#new(): "#{value}"|
      end
      true
    end
def validate_value(value)
      unless value.is_a?(String)
        raise TypeError, "can't convert #{ value.class } into PryTheme::HEX"
      end
      if value !~ PryTheme::HEX::PATTERN
        fail ArgumentError, %|invalid value for PryTheme::HEX#new(): "#{value}"|
      end
      true
    end
Validates whether +value+ is a valid hex colour value.

 @param [String] value
 @raise [TypeError] if +value+ isn't String
 @raise [ArgumentError] if +value+ is malformed
 @return [void]