Reversed and extreme sexual dichromatism is rare in parrots, where the sexes usually look alike. In eclectus parrots the difference is total: no shared plumage colour, and different bill colours as well. Nineteenth-century collectors working from trade skins had no way to link them, and the two forms were described independently.
The colours make sense against the nesting biology. Females spend long stretches inside tree hollows, competing intensely for scarce suitable cavities and remaining at the entrance where red is conspicuous from above against the dark hole. Males forage widely over the canopy, where green is cryptic against leaves. The favoured explanation ties the pattern to competition for hollows and to differing predation exposure.
The taxonomy has changed. What was long treated as one widespread species is now generally divided into several, including separate Moluccan and Papuan species, so older sources describing a single Eclectus roratus across the whole range are out of date.