Help needed: Identifying use of Tan M1

[TsrorsT]

Hello everyone,

I recently added a new helmet to my collection, an M1 hand brushed in tan! While I have no doubt this will be a mainstay in my corner of repaints, I would certainly like to attribute it to an actual use in its years of service. I will attach plenty of photos below in addition to a few theories brought up elsewhere that I think may hold some ground. 

A quick anatomy: a McCord Corp steel pot with an early Vietnam liner with a contract number stamped to the fiscal year of 1966. Green painted chinstrap hardware, so possibly even a KW era McCord, how cool is that!

I've had two plausible theories brought up already: a patrol boat lid possibly used in the latter half of vietnam, though this is more based on a greyscale image that shared the tone of the helmet in question. Nothing rock solid. 
The image: 


The second comes from a veteran who attended basic in the '60s, he remarks having seen all the helmets and E-tools having been laid out and painted a similar color of yellow by a nearby training company. 

Any more speculation or hard evidence would be very much appreciated! 😁