Tricky is right. I've found semi shaded area get them more purple. High light makes them brown, but you cannot argue with the above. I've seen great color in them in high light tanks, just not my own. CFP's! (Crazy F-in' Polyps!)
My advice, cut up your colony into three and put them in three different areas of the tank (high, low, middle, etc.) and see what works for you. Then, reunite them when you find the cherry spot.