Planet of Origin: Supposedly a planet oribiting the star Rigel
The Rigellians are a sentient vegetal species with some animal traits which developed a spacefaring civilisation in the 3rd millenium and were then a bit more advanced than humanity. They are known to turn from green to violet when afraid.
Source: Beyond Infinity, by Nat Schachner Aka Chan Corbett, in Astounding Stories, Jan 1937.
The story tells of a series of invasion that befell Earth starting in 3195, as the universe unexpectedly starts to collapse on itself and the surviving species rush toward the worlds who are still unaffected by the phenomenon to delay their extinction. The Rigellians were the first of a wave of invaders that attacked Earth, arriving in 3207, as a migration fleet of thousands of spaceships fleeing more advanced species which had invaded their own world. They landed in the jungles of Matto Grosso and eradicated more than a billion people before being themselves destroyed.