I have found the Blue Iris to be a fairly slow grower, especially early on. My frag has been through several changes, including upgrade from 55 gal to 125 gal tank, then switching from MH to T5 lights, etc. It's color has been quite variable, moreso than most of my other SPS that went through all the same changes.
Here is the frag I got from my LFS in September, 2009:
Here it is 5 months later, before the tank and light changes. It lost all of its green, which was sad, but it was a striking blue color. Not a whole lot of growth by this point....
Here it is today, almost a full year after the previous photo, a little over 16 months since I got it. It has picked up its growth rate, especially over the last several months. I really like the cobalt blue ends of the branches. The base of the branches and encrusted part have been tan/yellow for the past 6 months or so. It is slowly starting to get a greenish hue to these areas now, although that doesn't show up at all in the photo. I am hoping to get that rich green back.
Overall, I like the Blue Iris. I think the less than ideal color it has is due to my system. I don't run any zeo, vodka, bioballs, etc. Since I started doing my water changes via wet skim, it and several of my other corals are showing some color improvement.