Heliopora hiberniana is more common than we thought

[Reef Builders]

Helioporacea is a pretty unique order of Octocorallia (soft corals), which was thought for a very long time to contain only one single species, Heliopora coerulea, the famous Blue Ridge Coral that incorporates copper into its skeleton. This coral is very common throughout the Indo-Pacific and is even dominant on many reefs. It is a very…
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[Mada]

I had read in Daniel Knop's book (The Successful Reef Aquarium 1998) that the blue color of the Heliopora coerulea skeleton is due to iron salts but in this article it says that it is due to copper salts.
Maybe there was a lack of knowledge at that time or maybe that was inadvertently a wrong translation.
I would first think of copper because it turns green / blue when it oxidizes but I wonder what's up.
Does anyone know something more about it?