Sun parakeets are easily recognisable by their characteristic rich yellow plumage and reddish-orange head markings. Juveniles display a predominantly green plumage with a little yellow and orange. The distinctive yellow plumage is attained in the course of 6–8 months, and the only remaining blue-green plumage of an adult is the tail and wings.
In spite of their colourful plumage, these birds blend in well with tree leaves. Therefore, their voice is important for communicating with other birds in the group, so the birds are very noisy and make high-pitched calls in flight.
Sun parakeets live in pairs or groups of up to 20 individuals. The usual size is 5 birds per group, and bigger groups only occur when there is an abundance of fruit.