if anything it looks like it colored up nicely.
Yep, it's coloring up well.
Very nice! The new growth on it seems to be very different. Is this what gives it its "rainbow" name?
The rainbow moniker actually refers to the colors of the coral. Usually rainbow acros have 3 or more colors to them, which this one is displaying currently. You can read more about some of the named rainbows here:
https://reefbuilders.com/2015/01/26/rainbow-acropora-sps-coral/
I actually have to glue this piece down soon. The plug was tucked into a hole, but a bivalve that I've never seen before took up residence there and pushed the plug out of the hole. I'll pry the bivalve and relocate it before doing so since I do like them.
Here's the one that pushed out the plug. Never seen a clear bivalve like this one before.
This is the oldest one in the tank and came on a mariculture colony. It started out only being 1/2" in size when I first pried it off. It's just slightly more than 1" now. Looks like some hitchhiking clove polyps also hitchhiked in.
Another one that came in on a maricultured piece that I pried off. Looks kind of like a winged oyster, but missing the wing. The setosa is making its way in that direction so we'll see if it engulfs it or not.