This is not the first time I've heard that people have trouble getting the Purple cross to color nicely, but it really surprises me. It was always one of the easiest corals to grow in my tank, and it was a real show piece. I didn't do anything special, just good water quality... at times not so perfect
I wouldn't put it too high up, it needs room to grow. If it gets happy it will be massive.
An old picture, it's the purple (blue) coral on the left.
