The color of deck tractors, moto-tugs, deck jeeps, cranes, and other vehicles is difficult to answer from photos. Comparatively few photos of the Yorktown-class (and other wartime classes) are known to be in original color. Fewer still show any deck tractors at all. There may be documentary evidence and Tracy White, who frequents this site, may be able to answer that question. Absence that, we can turn to photos of other contemporary ships for an answer, such as Essex-class and Independence-class ships.
Photos taken during the war of Essex-class ships indicate that deck tractors and jeeps on board probably varied in color, either gray or olive drab. This may be due to who procured the vehicle under which contract. Different services (Army, Navy) had different equipment procurement responsibility at that time. In other words, one service would be responsible for procuring all of one type of equipment for all services. For example, the Army would be responsible to procure M1 helmets for all services. If the equipment was sourced under an Army contract, it would come painted olive drab and normally be put into service in that color. Likewise, if the equipment was sourced under a Navy procurement contract, it was likely to arrive gray and serve in gray. This means that it is possible to have a gray Navy-procured tractor or moto-tug next to an olive drab Army-procured jeep on the same deck at the same time.
In the first photo shown below, notice that the jeeps appear distinctly darker than the tugs. The jeeps may be olive drab and the tugs may be gray but it is very difficult to know with any certainty from the photo.
Complicating the issue, crews could repaint the equipment to any color if locally directed to do so.
Unfortunately, surviving color photos aren't very helpful; typically, no deck equipment is visible in the photos. And for those few photos where deck equipment is visible, the photo is in black and white, so no joy (see examples below).
Hopefully, Tracy can provide some help in answering your question. Ultimately, it's your model. Paint the equipment to your liking.
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CV-17 Bunker Hill 1945_4 318341084_5973722815980745_8973806155788792694_n.jpg [ 46.03 KiB | Viewed 1929 times ]
Regarding
Hornet's colors, the Trumpeter painting guides are a bit off. The sides of the real ship itself were painted in 3 colors: a dark blue, a medium gray (called "ocean gray") and a light gray (called "haze gray") with blue and ocean gray on the hull and ocean gray and haze gray on the island. Trumpeter drawings show only 2 colors, not 3, and the pattern shown in Trumpeter drawings does not match photos of the actual ship. Photos below show the three colors well and the actual pattern.
And yes, evidence suggests that what appears to be a white bow wave is merely worn away paint exposing the primer below (see bottom 2 photos). The actual, official painting scheme used by
Hornet, called a "measure", did not include a false bow wave.
Hope this helps!