This was clearly stated
This is a 3.3 V Arduino, thus no voltage divider was used on the Rx input. (Necessary with the 5V model.)
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Each LED in an RGB LED has a different forward voltage drop; I would use correct resistor values for each one depending on the RGB LED datasheet to balance the intensity and limit current as required.
What’s the real point of « balancing the intensity »?
(I get the concept but it has no practical use since human eye does not perceive RGB intensities in the same way. That’s what should be taken into account more than forward current and protection alone if you want to match the RGB choice)