It’s a form of stainless so doubtful it’s rust but more likely discolouration from welding heat.
(although it’s stain-less not stain-free)
F9 legs have crush sections within plus a bit of flex perhaps. The thing is F9 i designed to land on earth and it’s associated gravity. Whereas a starship designed to land on the moon will encounter much less gravity and therefore “should” have a softer landing – so it will probably have a different leg design.
Anyway, as already stated, these legs are sacrificial and probably quite a way from the finished article.