I've only ever seen blue Linckia myself but they do appear in red, purple etc (I believe there's some taxonomic debate as to whether these are separate species or just colour variations); Linckia are pretty common in the tropical Pacific so that's what I guessed at.
After checking my books, and also that Database, I concluded it was Leiaster, (probably speciosus) although I could'nt find a definite range for the species - everyone just said "Western Pacific".
Actually this is not a starfish... but two starfishes. The red arms of the Leiaster and the quarter of a cushion star (Culcita sp) occupying the upper left corner of the photo)