The simplest expanation of the Nimitz Graybook is in the first page.
Volume 1 begins 7 December 1941.
Rear Admiral Husband E Kimmel was CINCPAC.
He was relieved of command on 17 December 1941 by Vice Admiral Pye.
On 31 December 1941 Rear Admiral Chester W Nimitz took Command as
CINCPAC.
He was immediately promoted to Admiral.
Below are the cover and first two pages of Volume 1.

In the early volumes document sheets are White, Pink, and Green.
Later volumes include a Yellow sheet.
Except for the White sheets,
** these definitions may be
incorrect **
White sheets are the Running Summary.
Green sheets appear to be tactical communications while
the Pink sheets concern high level communications.

The first three GREEN sheets
in Volume 1 are in
Page 2.
The Helena is mentioned in the first one.

The Nimitz Graybook came to my attention in 2014
from John Szalay
These volumes have proven to be of considerable use
in all aspects of the War in the Central Pacific