Can corals be dyed?

[my2rotties]

I purchased an encrusting green/blue monti and it has turned white/mauve over time. I also had this sick looking incandescent green/purple acro, and it has turned mauve as well. Then there was the neon purple encrusting monti that has also turned mauve. The reason I purchased them is because of the bright sick colours, and although colours do fade at times... this is such a radical change from what they used to be I wonder if they might have been dyed. I have heard from a couple of people that they had the same pieces change colours as well...these people are very experienced reefers and I know if it is happening to them... maybe it might be dyes on the corals.

Any insight? I don't want to cause problems, but I want to avoid paying a premium price for something and have it turn into something less then standard. I know there are factors that can cause corals to bleach, but a few of these pieces have gone from one colour to a totally different realm. To have something go from a crazy green to mauve is odd. Or to go from green/neon blue to white/mauve is nuts.

Hoping to get some sort of answers to what might be happening or if any people have experienced this as well.