question re. Japan's war in color

[YW]

Dear all,

I wonder if people here can help me with the documentary, Japan's War in 
Color.  It's built on WWII footages shot in color.  Does anybody know 
the kind of color technique(s) being used, who shot the footages, why 
they were shot in color, and finally, why they have remained unseen for 
so long, and how they were discovered.  And have the Japanese filmmakers 
done anything with these footages?

Any comments and leads will be deeply appreciated.

Thank you!

Yiman Wang