"Hawaiians would never name anything as simplistically as "white mountain"."

Ha!  You must not be familiar with the Hawaiian language.  There are many words that are very, VERY simplistic.  Language is a form of communication, so the easier it is, the more people can use and understand it.  I'm not saying that Mauna Kea is "correct," just that it's not beyond the realm of possibility that the first person to name it would call it something like that.  We don't have to mysticize our history.  We can remember that these were humans doing things that humans normally do.  It's also plausible that different people gave it different names, given that Mauna Kea probably did not have the same significance to everyone on every island.  Mythologies and stories could be broken down to even the smallest of villages.   Was Maui on Oahu or was he on Maui?  Haleakala Maui or in Nanakuli?  Differing accounts, like all mythology.  Was it created by Wakea or did Maui fish it out of the water?