Nothing, Murray darlings, coastals, diamonds and jungles are all the exact same species, Morelia spilota. The only major differences between these are colouration and a bit of variation in size from a specific locality.
Depending on who you talk to and what view you take, these locality differences can represent distinct sub-species within M. spilota, or they just demonstrate variation along a cline within an extremely variable species. From what I know, the genetic analyses completed so far show no major differences between the different 'sub-species' lending support to M. spilota just being a single highly variable species. Further analyses are being conducted (and may be completed, the phylogeny of Morelia is not something I'm particularly interested in) to determine what is occurring within M. spilota.
Hopefully this answers you question and makes things a little clearer.
Cheers, Cameron