It appears from the accounts that the mole on Hazrat Mahdi’s (as) cheek will resemble a pearl and be as bright as a star, in other words very light in color:
There is a mark on his [Hazrat Mahdi’s (as)] cheek, reminiscent of a pearl, illuminating his face like a star. (Al-Barzanji, Al-Isha'ah li-ashrat al-sa'ah)
Hazrat Mahdi (as) has a thick beard, bright front teeth, a mole on his face, and a broad forehead. (Mari’ bin Yusuf Karami Hanbali, Fawaid Fawaid al-Fikr fil Mahdi al-Montazar)
He [Hazrat Mahdi (as)] will have a mole on his face. (Ibn Hajar al-Haythami, Al-Qawl al-Mukhtasar fi `Alamat al-Mahdi al-Muntadhar, p. 41)
There is a mole on his [Hazrat Mahdi’s (as)] face. (Al-Muttaqi al-Hindi)
The presence on the cheek of A SIGN ENLIGHTENING the face LIKE A STAR, REMINISCENT OF A PEARL, of Hazrat Mahdi (as) has been reported in the hadiths. Not only the word “mole” is used for this feature of Hazrat Mahdi (as), as all the features of this mole have been described. Terms such as “reminiscent of a pearl,” “like a star” and “illuminating” provide great detail about its shape and color. All this information shows that THIS MOLE WILL BE THE COLOR OF SKIN and not dark.