Every tank is different and will produce different growth and colors. I have never counted ours except the first few polyps that grew. It took a bit for them to settle in but after about 10 or 15 polyps they grow steadily and we have had to sell multiple large colonies to keep it cut down to size. Here is an older pic of our green ones. We have the brown ones too. The brown ones get larger and one is even splitting in half right now, I thought that was cool.
Lighting plays a huge role in the pattern and coloration of our grandis. I would start them on the sand and play it from there depending on which placement gives you the best results.