A couple of things I can offer...
150 watts halides are not a lot of light, maybe even at any depth. I would definitely "slowly" raise the photoperiod to maybe 8 hours over a month. Also, blue acros are some of the hardest colors to bring out. One of mine took a year before it started to even grow, let alone show its' true blue pigment. IMO they need the cleanest of water compared to some of the other colors.
Aside from this, could you let us know if this is a aquacultured, maricultured or wild acro? I've had a few maricultured pieces over the years and they seem to be a 50/50 gamble on whether or not they'll ever show their colors. My most blue coral is an ORA Roscoe's Blue. It was the smallest frag in my tank over a year ago, and now is as large as an orange. Sometimes the genes of the frag you have matter too. Most aquacultured pieces have been through the rigors and insults that we reefers make when trying to mimic mother nature. They've built up some immunity to less than perfect water conditions and a host of different lighting schemes. Over time, some maricultured and wild frags can grow to be beautiful pieces that do very well for reefers later on down the line after a few generations of frags have been established in captive systems.
Another thing that really brings out the blues is actinic lighting. Since you run 150 watt bulbs, I don't know if you'd want to lower the par of the bulbs by going to a 20k, but some supplemental actinic lighting can do wonders for making some blue and purple acros color up.
