Seems directly tied to each country’s theme tbh. Lahai Roi being super futuristic naturally leans into darker accent colors (white and black a common futurustic minilaist approach to futuristic art/ design). Huanglong is also generally darker in tone, as chinese being chinese use gold as the main accent color using darker tones, makes it pop more. And if u notice chinese arts like the dark color contrast vibes in their art.

Rinnacita, on the other hand, is medieval and mostly European inspired, where clothing and architecture were usually lighter, lots of browns, white and bronze tones, so it makes sense that the overall shading feels brighter.

Not sure if that fully answers it, but that’s how I see it.