IRC the ones assigned to the Navy were grey/ gray , the USMC ones green & camo
No, that's not correct. All amtracs and amtanks were initially painted Ocean Grey. However, this faded to a light blue and both the Army and Marines complained about it being too conspicuous once the vehicles were ashore. As a result, from May 1944 existing vehicles began to be repainted in Olive Drab and new vehicles were painted this colour in the factory. In the interim, some units painted camo over the Ocean Grey (usually a sand colour).
LVT(A)-4s on Saipan were painted Ocean Grey (i.e. they went into action before the switchover to OD). Army vehicles had quite prominent white stars, but Marine vehicles didn't.
This is from Zaloga and Balin "US Amtracs and Amphibians at War 1941-45".
