Taken in Bonaire last month, I think this may be an intermediate or juvenile phase Blue Parrotfish. It has the right shaped head and tail, large scales and yellow fins but the main body colour seems a bit iffy although there is perhaps a faint purplish tinge as described in Humman and Loach's book. However, all parrotfish juveniles seem to vary quite a lot and they are a bit of a minefield to me.
Can anybody confirm/deny/suggest an alternative please?