def []=( num, value )
      closed!
      if (num < 0 || num >= @leds.length)
        raise IndexError, "index #{num} is outside of LED range: 0...#{@leds.length-1}"
      end
      @leds[num] = to_color(value)
    end
def []=( num, value )
      closed!
      if (num < 0 || num >= @leds.length)
        raise IndexError, "index #{num} is outside of LED range: 0...#{@leds.length-1}"
      end
      @leds[num] = to_color(value)
    end
Set the LED at position `num` to the provided 24-bit RGB color value.

 Returns the 24-bit RGB color value.