I heard from many hadiths that Umar Ibn al Khattab (RA) was dark skinned while there were others that explained he was light skinned but after the famine, he consumed nothing but olive oil which shifted his skin tone. Does anyone know the true answer to this question? I know in the show on MBC, there is a white actor that plays him.
'Umar ibn al-Khattab is known to have been a very tall (he was described as having the hight of a riding person) white skinned man. Historians reported that his skin became darker during the time of famine some like al-Waqidi said it was due to the consummation of oil.
Here a quote from imam a-Dhahabi's siyar 'alaam an-Nubalaa' سير أعلام النبلاء:
In the following I've translated from Arabic language as these translations are of my own take them with the necessary care!
وَعَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ قَالَ : كَانَ أَبِي أَبْيَضَ تَعْلُوهُ حُمْرَةٌ ، طُوَالًا ، أَصْلَعَ ، أَشْيَبَ .
And on the authority of Abdullah bin Omar, he said: My father was white, with a reddish complexion, tall, bald, and gray.
وَقَالَ غَيْرُهُ : كَانَ أَمْهَقَ ، طُوَالًا ، أَصْلَعَ ، آدَمَ ، أَعْسَرَ يَسَرَ
Others said: He was albino, tall, bald, of a dark skin, left-handed and left-handed.
And as-Suyuti quoted in his Tareekh al-Khulafa' تاريخ الخلفاء the following:
أخرج ابن سعد و الحاكم عن زر قال : خرجت مع أهل المدينة في يوم عيد فرأيت عمر يمشي حافيا شيخا أصلع آدم أعسر طوالا مشرفا على الناس كأنه على دابة قال الواقدي : لا يعرف عندنا أن عمر كان آدم إلا أن يكون رآه عام الرمادة فإنه كان تغير لونه حين أكل الزيت
Ibn Sa'ad and al-Hakim reported that Zer said: I went out with the people of Madinah on the day of 'Id and saw 'Umar walking barefoot, a bald man, Adam (a dark skinned man), for a long time, towering above the people as if he was on a horse. Al-Waqidi said: It is not known to us that 'Umar was Adam unless he saw him in the year of famine, because he changed color when he ate oil
و أخرج ابن سعد عن ابن عمر أنه وصف عمر فقال : رجل أبيض تعلوه حمرة طوال أصلع أشيب
Ibn Sa'ad narrated on the authority of ibn 'Umar that he described 'Umar, so he said: A white man with a reddish complexion tall, gray bald man
و أخرج عن عبيد بن عمير قال : كان عمر يفوق الناس طولا
And it was narrated on the authority of 'Ubayd bin 'Umair that he said: 'Umar was longer than people
و أخرج عن سلمة بن الأكوع قال : كان عمر رجلا أعسر يعني يعتمد بيديه جميعا
And narrated on the authority of Salamah ibn al-Akwa', he said: 'Umar was a left-handed (A'sar) man, meaning he was dependent with (using) both of his hands together
و أخرج ابن عساكر عن أبي رجاء العطاردي قال : كان عمر رجلا طويلا جسيما أصلع شديد الصلع أبيض شديد الحمرة
And ibn 'Asaker narrated on the authority of abu Rajaa' al-'Uttardi who said: 'Umar was a tall, massive, (very) bald man, white with an intense reddish compelxion.
Finally note that the term used to describe the darkness of his skin in all these sources was:
The term Adam is usually refers to a dark brown not black skin as it was mentioned in a hadith describing our prophet ():
I heard Anas bin Malik describing the Prophet (ﷺ) saying, "He was of medium height amongst the people, neither tall nor short; he had a rosy color, neither absolutely white nor deep brown; his hair was neither completely curly nor quite lank. Divine Inspiration was revealed to him when he was forty years old. He stayed ten years in Mecca receiving the Divine Inspiration, and stayed in Medina for ten more years. When he expired, he had scarcely twenty white hairs in his head and beard." Rabi`a said, "I saw some of his hairs and it was red. When I asked about that, I was told that it turned red because of scent. " (Sahih al-Bukhari)
Finally from a scientific point of view such color changes are not far fetched: For example a paleness might come from to the lack of iron or folic acid, if the liver is sick one would turn to a yellow color (happened to me when I had hepatitis) , the lack of the vitamins B3-B12 could turn the skin color brownish. And actually the famine was a reason for not consuming meat products which are rich on this vitamins.
In my first answer I asked for some links to the hadith's in question. As it is, I've discovered them myself. According to Hadith scholars the narrations referring to Ibn Khattab complexion have described him from pale, to pale with reddishness, brown and wheat coloured to dark brown.
This wide difference suggests that the narrators had widely differing terms for colours rather than his complexion being so varied ... It's well known that in pre-industrial societies there were wide variations of terms in a language since there was no tv or newspapers that helped form a language standard and language was highly localised.
Then one speaks of a dialect continuum of a language. In fact, it was research into the Qu'ran and its language that helped bring about a standard form of Arabic - Classical Arabic.