Is the "redness" referred to in the Hadith: "Eat and drink until the red [light] appears to you" the redness that precedes sunrise, or the white light that appears across the horizon at the beginning of Fajr prayer?

The noble Prophetic Hadith (definition) clarifies the false dawn (al-fajr al-kadhib) and the true dawn (al-fajr al-sadiq). The false dawn is the elongated whiteness which does not prohibit eating and drinking. The true dawn is the transversal (reddish) whiteness at which eating and drinking become forbidden. The differences between them are: The false dawn is followed by darkness, it is elongated, and there is darkness between it and the horizon. Whereas the true dawn only increases in brightness, it is spread out, and there is no darkness between it and the horizon.