Does it display green fluorescent if you switch it to the blue moonlight?
I would wager a guess that it is a lack of light. That is not a powerful light. If the toadstool is a morph/species that is the same as mine (and it looks like it) than the flesh should be a light cream color along with bright green polyps.
You could try moving it to the taller rock on the right and observe for a couple weeks. (IMO, it would look good attached to the shadowed part on forward left on the top there, pictures can deceive though)
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