sade1212 said:

Cutting Luke’s lightsaber entirely wouldn’t add anything to the film, but I’ve been tempted to try to VFX it to be his ROTJ saber. I’m torn between the symbolic importance of the blue lightsaber being the same one that he previously rejected, and the fact Luke otherwise seems to be aiming to appear to Kylo as Kylo would remember him. For all of Kylo’s thirteen years of training at Luke’s Jedi temple, his master had a green lightsaber - we know this since Luke uses that same saber in ROTJ and in the TLJ flashback. And yet, when Luke appears to Kylo again and ignites his saber, it’s blue. Surely Kylo would immediately spot something was up, since every other time he’s ever seen Luke ignite his saber, it’s been green. I mean, the audience notices Luke’s saber colour change ESB to ROTJ, right? It’s a glowing laser sword, it’s not subtle. And if Kylo notices Luke’s saber is now blue, he’d probably glance at the hilt, realise it’s the saber that just got split in half, and suspect Luke is up to something. It risks giving the game away and having Kylo realise he’s being played.

https://www.youtube.com/watch?v=QwWrmSP65lM