I bought a small male from my lfs around 7 months ago. The only yellow it had at the time was on the tail and that was barely visible and the throat had a small tint of blue. For the last 6 months or so I figured it was a male but just not very brightly colored yellow fins and still a hint of blue. About a month ago I started to notice the yellow on the tail growing in size along with the blue on the throat. Fast forward to now and the tail is bright yellow, the throat is really blue and the top and bottom fins are outlined in yellow ( never even had a hint of yellow on those). I haven't changed anything as far as water change interval, dosing etc..... it was very shy at the lfs and for the 1st 4 months or so but a couple months ago it decided life wasn't to bad in my reef and none of his buddies were gonna hurt him and he is always out and about and even eats from my hand, and doesn't even hide when I'm doing maintenance inside the tank. I wouldn't sweat it and just be patient.