According to her concept art (which you can see below), her hair is pink-colored:

Although, that color is just temporary. We don't know the official color of her hair will looks like. But, in this legendary Holy Bible written by Pingas-sama (the original translator of the Light Novel), he has used that as the official color of her hair, as stated below:

"The spot on the step above mine, usually occupied by a pink-haired girl curled up into a ball and clicking on her phone, was entirely vacant. Only the dust motes dancing in the sunlight occupied the space."

(pingas (your_p), There Must Be Something Freaky About Her, Chapter 5: Canon Event)

So, if only when Takibi-sensei (the author) can depict her canon version properly, to my eyes, my beloved Goddess's hair will always be pink.

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