You have a Discosoma sp. mushroom, which can change color that will vary with lighting and water quality. I have some Rhodactis sp. mushrooms that were bright green when I bought them, and are purple in my tank.
IMO, it's a lighting thing. Higher light will give one color, dimmer light will give another color. They don't need as much light to survive, and too much light can be detrimental, so if you like that color I'd keep them there.

Just a thing that happens with them, and is common.
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-Lindsay
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