Sallow: (adj) of an unhealthy yellow or pale brown color. From the Old English salo ‘dusky’.
"In 2017, a genetic study of 96 various Scythian samples [found] that Late Bronze Age and early Iron Age Scythians harbored nearly exclusively European-related ancestry, close or identical to the earlier Sintashta, Andronovo, and Afanasievo cultures..."
Yes, and the Rhun fought in Sauron's army. They were the bad guys, not the good.
Kublai Khai was two generations after Ghengis; genetically entirely different from him. I can give you references for this if you wish.
1. "adjective, sal·low·er, sal·low·est.
of a sickly, yellowish or lightish brown color:"
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So yellow is dark skinned to you? Light brown people (eg. Italians or Mediterraneans) are dark skinned now? People from China or Japan are dark skinned? Sallow, eg. sickly yellow or light brown, especially if referring to East Asians, is still light skinned.
2. Europeans =/= Germans. The two terms are not interchangeable. Europeans are a vast group of diverse people who spoke many different language families and language groups. Germans are a very specific branch of European people who speak a Germanic language and/or are descended from Germanic speakers. The Iranian Scythians belong to an even more vast group called Indo-Iranian-Europeans. The groups of people referred to in your wiki article - the Sintashta, Andronovo, and Afanasievo cultures are proto-Indo-European people who migrated into Europe, India, the Middle East, etc.
"From the Sintashta culture the Indo-Iranian followed the migrations of the Indo-Iranians to Anatolia, India and Iran" -wiki
Scythians of different regions also have different influences:
"In 2017, a genetic study of various Scythian cultures, including the Scythians, was published in Nature Communications. The study suggested that the Scythians arose as admixture between European-related groups from the Yamnaya culture and East Asian/Siberian groups. While the origin of the Scythian material culture is disputed, their evidence suggest an origin in the East. Modern populations relative closely related to the ancient Scythians were found to be populations living in proximity to the sites studied, suggesting genetic continuity."
"The shift toward the Iranian-related gene pool is found as early as ~650 BCE in one Eleke_Sazy_650BCE individual (ESZ002) retrieved from an elite Saka burial, while three of four individuals from one of the earliest Tian Shan Saka site of Caspan_700BCE fall within the Tasmola/Pazyryk cloud."
3. Rhun are not dark skinned people. If they're sallow then they're light skinned. Gondor also has swarthy skinned people. So that disproves your claim that darker/dark skinned = bad in Lord of the Rings.
4. Kublai Khan was descended directly from Mongolian nobles and Mongolian wives. That means he is genetically similar to Genghis Khan and would have looked like Genghis Khan. Kublai Khan's father was Genghis Khan's son, and his mother was another Mongolian woman. Mongols who marry Mongols will have children who look like Mongols.
I can give you more references to Kublai Khan's lineage if you wish. The Mongol lineage were carefully recorded and it shows him being descended from Mongolians of the time.
And the actual painting of Mongolians in the 1200s AD portray them as similar to modern day Mongolians. Not just the painting of Kublai Khan, but others too. There are also paintings of Ogedei Khan, the direct son of Genghis Khan and a Mongol woman, portraying him as a Mongol looking dude not much different from modern Mongolians. Look up the Yuan era painting of Ogedei Khan.
https://www.newworldencyclopedia.org/entry/Ögedei_Khan
I'm thinking you are probably confused by anchronistic Persian references to blue-green colors that created a conspiracy that Genghis Khan was somehow European looking. That is a later Persian writing that mistranslated the honorary title "blue wolf" into a physical trait. There are also references to some Mongols with red hair, because red hair also evolved in Eastern Eurasia and exists naturally among some Central and East Asian populations in China, Mongolia, Korea, etc. Neanderthals, Europeans, and Central & East Asians all have genetic mutations for red hair. These genes either evolved independently or may have been inherited from Neanderthals. Some very dark skinned Africans and Australian Aborigenes have natural blonde hair, so these traits are unpredictable.