How many protons does phenolphthalein lose in basic solutions?

So, I've looked it up and Wikipedia claims that two protons are released by Phenolphthalein when pH is over 8.2, but I've seen other sources that claim only one proton is lost. So, is it really just one or two? Which form is responsible for its colour? (I would expect a fully deprotonated PhPh in more basic solutions, so I guess the PhPh that released two protons is the one responsible for the solution's colour)

• Can you please cite the "other sources"? Their context may be different, for example, they may lose only one proton in stronger acidic conditions. – Gaurang Tandon May 3 '18 at 1:37

ChemSpider phenolphthalein's $\mathrm{p}K_\mathrm{a}$ value: 9.7 (at room temperature). Here they've is only given one $\mathrm{p}K_\mathrm{a}$ value, but it is still reasonable to assume that there are other forms in other pH conditions, like in this image: