The yellow lightning was meant for a ‘Rey Nobody’ version, to distance her from Palpatine, with the added meaning of her saber being incorporating or accepting her shadow. But the majority opinion seems to be that blue is better, even for that alternate version.
Related: For the regular Rey Palpatine version, should Palpatine’s fingers crackle when we first see them? Might just remove it in both versions. Why make it any more obvious than it already is when Rey shoots lightning what the reveal is gonna be?
“Why did the Emperor come for me? Why did he want to kill a child? Tell me.”
“Lol, didn’t you figure it out when you shot lightning? You’re Dooku’s great-granddaughter’s sister.”