I agree with you, but to play devil’s advocate, the blue one symbolizes Luke accepting Rey’s request for help (and his “role in all this”) that he rejected by tossing that same lightsaber aside at the beginning of the film, so changing it to the green one would lose that bit of symbolism.
To play devil’s advocate to your devil’s advocate… I think it is more symbolic for the green one to be used as it shows Luke has grown past his mistakes and is ready to take on the role “burden” of being a master once more and has “let the past die” as he overcame his moment of weakness and will eliminate Kylo for the right reasons now. I get that the blue is a hint that he isn’t there but the footwork on the salt and the wink at C-3PO do that enough, since Threepio can scan life forms and would know that he wasn’t actually there, hence the wink. Since I’m ranting on… I would like to see Hal include Luke’s shoulder dustoff in his edit. I get that it is a little over the top, but I take it that Luke is so done with Kylo’s s*** and wants to rub it in that he is more powerful, adding even more to Kylo’s anger.