Acropora changing color

I recently installed a 250 Watt double-ended HQI light in my 150
gallon reef. I have noticed that quite a few of the Acropora frags
that I have obtained are changing from their original color (yellow
and purple) to a green fluorescent color. The new color doesnt look
bad, but I am disappointed to lose the original coloring. All the
frags I have obtained were grown under 400 watt MH, prior to being
placed within 10 inches of my 250 watt HQI bulb. All frags appear to
be extending polyps, and are exposed to intermittent current. Further
I can see that the frags are growing at the bases. Does the color of
Acropora frequently change, and will the original color return if the
lighting matches the conditions it was originally grown under?