It is reported that the Prophet Mohamed (pbuh) said, (In a dream) I saw myself following a herd of black sheep. Then a group of white sheep came (and mixed with the black sheep) until they (the white sheep) became so many that the black sheep could no longer be seen in the herd of sheep." Abu Bakr, the companion of the Prophet (pbuh) and the interpreter of dreams, said, "Oh Messenger of Allah. As for the black sheep, they are the Arabs. They will accept Islam and become many. The white sheep are the non-Arab Persians, etc. They will accept Islam and become so many that the Arabs will not be noticed amongst them." The Prophet Mohamed (pbuh) then said that an angel had interpreted the dream the same way.
Zaid ibn Aslam related that the prophet (SAWS) saw a vision and told his companions about it. He said, "I saw a group of black sheep and a group of white sheep then mixed with the black sheep. I interpreted it to mean that the non-Arab Persians will enter Islam and then share with you your genealogy and your wealth." The companions became surprised by what he (SAWS) said. Then one said, "The non-Arab Persians will enter our land, Oh Messenger of Allah?!" The Prophet (SAWS) then said, "Yes. By He Who Has my soul in His Hand, if the religion was hanging on the distant star, men from the non-Arab Persians would reach it and the luckiest of them would be the people of Faris.
The Prophet Mohamed spoke the truth and this is why there is this misconception concerning the appearance of the original Arabs. This is why the original dark-skinned Arabs are not clearly visible today.