Analogous color schemes
Let us first look at the pirates who are travelling in a bronze, goose-shaped airship:
As the image above proves, this bronze color is a lowly saturated shade of medium dark red.
The pirates' clothes are dyed in shades of different reds. Among the various reds there is contrast of value (light and dark) as well as saturation (highly saturated headgears vs lowly saturated controls).
|12-part color wheel according to Johannes Itten (1961)|
These analogous colors look warm and fresh in contrast to the blue sky against which they are often seen during flying scenes. Here, they wear gloves, guns and headbands that are closely related to the sky color:
Inside the ship, however, green is used to balance the predominantly red and yellow scheme. It is noteworthy that the green leans towards yellow rather than blue and thus emphasizes the warmth inside the ship.
To simplify orientation, Pazu's side of the table (where the pirates sleep) is still in the darkness while Sheeta's side (she comes from the bright and warm kitchen) is in the light. Because of the curtains there is no outside light leaking in.
Before Sheeta enters Dola's bedroom, her beige nightgown distinguishes her from the pirates. After she comes out, her highly saturated pirates' dress visually ties her to the pirates.
It is worth looking at Dola for a moment: In terms of color, the pirates' mother and outspoken leader is singled out by her dignified dark blue dress that fits her age and maturity far better than the boys' candy colors. Her salmon colored "Pippi-Longstocking" braids not only fit her flamboyance but also connect her to the rest of the pirates. Compared to the boys' clothes there are not only strong contrasts of value and saturation but also of hue (yellow headgear, blue dress) in Dola's clothes.
Unsurprisingly, her room reflects all the colors of her appearance and from the painting on the wall we can assume that Sheeta gets to wear the very harem pants that Dola wore as a young buccaneer.
Camouflage and Identification
The less agreeable opponent in the children's race to find the flying city is the army. Before WWI, uniforms were brightly colored for identification and display in the field. Since Laputa takes place in a fictitious Wales around 1900, the uniform design is inspired by such full color tunics that were common before utilitarian camouflage uniforms came into fashion.
Nevertheless, these soldiers look familiar to contemporary audiences because their tunics are "military" green which fulfills modern camouflage requirements quite well. In many of these green-dominated shots and scenes, red spots are used for balance as well as identification of rank.
Not only medals but also colored epaulettes indicate different ranks and types of soldiers. Regardless of military hierarchy, the lack of contrasting colors on the lighter green uniforms of the soldiers behind the general makes them seem less important (though also mustached) than the bald general who is obviously reporting to Musca who in turn is characterized by brown throughout the film:
As we have seen in a previous post, Musca's henchmen often blend in with dark bluish grey (and often shady) areas of the background.
But back to the colored epaulettes: the low-rank infantry soldiers's uniforms are balanced by red epaulettes:
As you may have noticed, mustard-colored yellow features prominently on the general's uniform as well. Towards the end of the film, this color is linked to the earthly treasures of Laputa. Visually, the army is very much at home in Laputa's treasure chest:
Because of their predominately green uniforms we recognize the soldiers even in extreme long shots:
And like differently colored armies on past battlefields, the antagonists are most clearly distinguished by silhouette and color from a distance:
The juxtaposition of red and green uniforms fulfills different functions: Although similarly organized and both pursuing the same objective of finding the flying city, the army and the pirates are clearly antagonists which is visually accented by uniform colors that are diametrically opposed on the color wheel.
Moreover these colors seem "right" on a more intuitive level since we are used to green military uniforms and flamboyantly vested pirates (from Gene Kelly and The Crimson Pirate to Captain Hook). Within the narrative it is no surprise that the pirate colors look more attractive and in keeping with their carefree childlike behaviour Dola's boys are surrounded by candy colors.
Basically, this post was all about contrast of hue. Neither value nor saturation are relevant to discerning pirates from soldiers. Overall, no lighting situation or color cast is visually favoring either red or green. Within the general color scheme they seem to be treated equally (neither the pirates nor the soldiers look foreign to the rest of the film).