A subspecies is an alternate version of a monster. These monsters are usually named for their new color—for example, Blue Yian Kut-Ku is a subspecies of Yian Kut-Ku. Subspecies are usually nearly identical to their original monsters, as, after all, they are the same species. However, they usually possess increased health and stamina, have altered weaknesses, and yield different carves.
Subspecies often sport new attacks and movement patterns, such as the Red Khezu's "neck swing" or the lightning attacks of the White Fatalis. Certain subspecies do in fact have altered physical features, such as the beard and larger hair spike on the Emerald Congalala, or the Diablos shell on the Plum Daimyo Hermitaur.
Golden Rajang is not actually a subspecies. It is an ordinary Rajang that looks almost golden while calm, and shows its Electric Aura in Rage mode. This is the same for the 3rd generation's Deviljho, which G-rank version always has its shoulder muscles red and has its face covered in Dragon, while the normal Deviljho only huffs this element during its rage.
