The women Tolkien described as beautiful seem to be either blond (Galadriel, Eowyn, Indis, Idril) or have the combination of dark hair and pale skin (Arwen, Morwen and Aredhel). For example, Arwen, the "fairest that now walks the earth", is described as having "dark hair" and "white arms".1 She is said to be the living likeness of Luthien, whom The Silmarillion describes as "the fairest of the children of Iluvatar". Arwen's blond grandmother Galadriel is implied to be comparable to Arwen in beauty as revealed in the discussion between Eomer and Gimli.2
Galadriel's own grandmother, Indis the Fair, is described as "golden haired" in the Silmarillion. Indis' great-granddaughter Idril was also described as blond and beautiful:
"But fairer than all the wonders of Gondolin was Idril, Turgon's daughter... whose hair was as the gold of Laurelin..."3
"...Idril the King's daughter... was as golden as the Vanyar, her mother's kindred, and she seemed to him as the sun from which all the King's hall drew its light."4
Aredhel, cousin of Galadriel, another "fair" lady, is described as follows:
"Ar-Feinel she was called, the White Lady of the Noldor, for she was pale, though her hair was dark, and she was never arrayed but in silver and white."5
3 out of 6 of the beauties mentioned in the previous section are described as tall. Finwe's wife "Indis the Fair" was "a Vanya... golden haired and tall..."6 Aredhel too, was tall: "when she was grown to full stature and beauty she was tall and strong."7 Morwen, "the proudest and most beautiful of mortal women in the days of old" 8, is described thus in Chapter 2 of the Unfinished Tales:
"Morwen.. was... of close kin to Beren One-Hand. Morwen was dark-haired and tall, and for the light of her glance and beauty of her face men called her Morwen Eledwen, the Elven-fair..."
In the author's mind, height seems to go hand in hand with nobility and importance, at least for human and Elven characters. Morwen is the wife of Tuor's paternal uncle. Tuor is the human grandfather of Elrond and an ancestor of Aragorn. Morwen herself is related to Beren, another human ancestor of Elrond and Aragorn. Morwen's daughter Niniel is described as follows:
"Tall and strong she seemed; for great of stature were those of Hador's House, and thus clad in Elvish raiment she matched well with the guards, being smaller only than the greatest among them."9
To add to the examples above, Galadriel, "mightiest of the Noldor"10, was described as "tall beyond the measure of even the women of the Noldor". Aragorn's heroic ancestor is Elendil the Tall. The Numenoreans, supposedly the noblest of humans, are also "taller than any of the sons of Middle Earth". Physical height is associated with racial superiority. The only exception that comes to mind is Hurin, father of Turin, who was described in Unfinished Tales as shorter than both his father and his son. Tolkien did not create many short human or Elven heroes. Perhaps Tolkien makes up for this height bias with the dwarven and hobbit heroes of LOTR.
In the Tolkien universe, it seems to be a compliment for a mortal to be described as resembling an Elf, a member of the most beautiful race. Sam's daugher Elanor is noted for her beauty and thus said to look more like an elf-maid than a hobbit. Noteworthy beauties among both human men and women are often described as Elven in appearance.
From Chapter 21 of The Silmarillion, we have this description of Turin Turambar:
"he was in truth the son of Morwen Eledhwen to look upon: dark-haired and pale-skinned, with grey eyes, and his face more beautiful than any other among mortal Men... Many called him Adanedhel, the Elf-man."
Here's another example - a description of Lalaith, Turin's first sister:
"Her hair was like the yellow lilies... 'Fair as an elf-child is Lalaith,' said Hurin to Morwen..." 11
Another account of a human beauty said to resemble an Elf comes from the chapter "Aldarion and Erendis" in Unfinished Tales. The following excerpt describes the reunion between Aldarion, prince of Numenor, and Erendis, his beloved.
Riding one day in the forests of the Westlands he saw a woman, whose dark hair flowed in the wind, and about her was a green cloak clasped at the throat; and he took her for one of the Eldar, who came at times to that part of the island...
Erendis' people also compared her to another human who was an Elf-lookalike - Morwen Elven-fair:
"... the people of Andunie, looking upon the blissful company, said that none were more fair than Erendis, and they said that her eyes were as bright as were the eyes of Morwen Eledhwen of old..."
Of the most evil Elf villain of The Silmarillion, and indeed of the whole LOTR universe, we have the following description: "Eol...is a tall elf, dark and grim, of the kindred of the Sindar..."12 It should be noted though, that Tolkien has described white-skinned people as "dark" because of their hair color. In The Lost Road and Other Writings, the Numenorean Herendil has a "white body" but is nevertheless considered "dark" by himself and his peers.13
On the topic of color differentiation, here's an excerpt from The Silmarillion, Chapter 18: Of the Ruin of Beleriand:
It is told that at this time the Swarthy Men came first into Beleriand. Some were already under the dominion of Morgoth, and came at his call; but not all... These Men were short and broad, long and strong in the arm; their skins were swart or sallow, and their hair was dark as were their eyes... Maedhros...made alliance with these new-come Men, and gave his friendship to the greatest of their chieftains, Bor and Ulfang. And Morgoth was well content; for this was as he had designed. The sons of Bor were Borlad, Borlach, and Borthand; and they followed Maedhros and Maglor, and cheated the hope of Morgoth, and were faithful. The sons of Ulfang the Black were Ulfast, and Ulwarth, and Uldor the accursed, and they followed Caranthir and swore allegiance to him, and proved faithless.
There was small love between the Edain and the Easterlings, and they met seldom...
It seems that even among Swarthy Men, the blacker ones turn out to be worse in character. And Gollum, degraded from his former hobbit-like state (hobbits are apparently not any darker than 'brown'), is described as a "thin black fellow".14 But how consistent is this "color stereotyping"? The demon Sauron has a "black hand", but then Saruman's white hand is also evil and cruel. But there is enough evidence to suggest that "dark appearance=evil, light appearance=goodness" is the rule in Tolkien's universe.
1. LOTR, p221 and Appendix A
2. LOTR, p953
3. The Silmarillion, p151
4. The Silmarillion, p163
5. The Silmarillion, p64
6. The Silmarillion, p69
7. The Silmarillion, p64
8. The Silmarillion, p283
9. Unfinished Tales, p121
10. Unfinished Tales, p241
11. Unfinished Tales p62-63
12. The Silmarillion, p163
13. The Lost Road and Other Writings, p66
14. LOTR, p721