Is that what's under his armor, something he's wearing over his armor or shapeshifting?
In the context of this comic I'm guessing the middle option is true.
It's the third option. KH disguises himself as an old man named Ziusuthra during the Babylon chapter of FGO. Coincidentally, Ziusuthra is one of the analogs to Noah in Mesopotamian myth.
RejectedI am done.Hey look!Should I just give up and put a wig on?This disguise is perfect right!?Ehhh?Reject-ed-edGramps, are you done with your disguise?Before infiltrating the party hallgramps...