It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The blessing of horses lies in their reddish (chestnut) ones, and the most blessed of them is the one with a white blaze on its forehead, white on its legs, and its right foreleg not white."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10631