I believe we can at least partly answer some of your questions, but the subject becomes much more interesting if one delves a little deeper. Here's what I've got:
Philippine Air Lines, at the outbreak of hostilities, possessed two Beech 18s, civil registration numbers NPC54 and NPC 56. In this illustration of NPC56, the company livery was red all over with stylised fuselage stripes in yellow or gold, probably along the lines of the Beech factory graphics.
In the above photograph of NPC54, the colour of the stripe also appears lighter than the fuselage but it is described as "broad dark fuselage stripe ending near nose as a large diamond enclosing "PAL", with fleet number "51" on nose" - but the colour of the fuselage is not mentioned. See:
Beech 18, NPC54 in the PAL hangar at Nielsen Field, with a Beech Model 17 “Staggerwing” in the foreground. Is this perhaps the Staggerwing commandeered by the Bamboo Fleet?
A photo of NPC 56 at RAAF Amberley Field in Queensland, Australia (January 1942) shows the aircraft to be without the stripes; probably repainted in olive drab with a light-grey underside and what appears to be a (skew) US military star insignia on the fuselage. See:
A Jacobs-powered Beech 18. Note the "helmeted" cowlings and factory-style graphics (similar to that of PAL's two Beech 18s). NPC54 and NPC56 were powered by Pratt & Whitney radials, therefore the flush cowlings.
This pdf also gives some detail of a Beech 18 of the Philippine Army Air Corps, delivered in April 1939 with olive drab fuselage and international orange tail and wings. It was powered by Jacobs radials – identifiable by "helmeted" cowlings. This aircraft was apparently destroyed at Darwin during the first raid of February 19th. NPC54 was destroyed on the ground at Surabaya on the same day, and the legendary "Pappy" Gunn was shot down (but survived) in NPC56 over Mindanao on 27th January 1942. General George C Kenney's book, "The Saga of Pappy Gunn" tells his story, the complete text of which can be viewed here: