Much clearer thanks!
If I understand correctly, you have the RGBA led, with which you can choose the light that's displayed through the hilt and blade.
Purely technically speaking, and at the same battery charge level, the brightness stays the same. Were you to measure the brightness in Lux or candles/m², it would (or at least should) be exactly the same.
However, some colours appear brighter to the human eye. Which means that a light green will SEEM less bright than a flaming red for example.
TL;DR: the colour will change, not the brightness.
Of course, if I am mistaken, please feel free to correct me fellow SF members.