Brave New World
How we cite our quotes:
Oh!" He gave a gasp and was silent, gaping. He had seen, for the first time in his life, the face of a girl whose cheeks were not the colour of chocolate or dogskin, whose hair was auburn and permanently waved, and whose expression (amazing novelty!) was one of benevolent interest. Lenina was smiling at him; such a nice-looking boy, she was thinking, and a really beautiful body. The blood rushed up into the young man's face; he dropped his eyes, raised them again for a moment only to find her still smiling at him, and was so much overcome that he had to turn away and pretend to be looking very hard at something on the other side of the square. (7.46)
So here's some insight into the otherwise difficult question of why someone with John's depth and principles would ever want someone as vapid (dull or flat) as Lenina. In a world where he has been forever different, she is someone who looks like him, that is, white and blue-eyed. John's immediate thought is companionship – check out his "Character Analysis" for more.
"For instance," she hoarsely whispered, "take the way they have one another here. Mad, I tell you, absolutely mad. Everybody belongs to every one else – don't they? don't they?" she insisted, tugging at Lenina's sleeve. Lenina nodded her averted head, let out the breath she had been holding and managed to draw another one, relatively untainted. "Well, here," the other went on, "nobody's supposed to belong to more than one person. And if you have people in the ordinary way, the others think you're wicked and anti-social. They hate and despise you. Once a lot of women came and made a scene because their men came to see me. Well, why not? And then they rushed at me… No, it was too awful. I can't tell you about it." (7.56)
Like Lenina, Linda is defined by her sexuality – the women are essentially mirror-images of each other, but they reflect the differences between their two worlds.
In those other words he did not understand so well, she said to the man, "Not with John here." The man looked at him, then again at Linda, and said a few words in a soft voice. Linda said, "No." But the man bent over the bed towards him and his face was huge, terrible; the black ropes of hair touched the blanket. "No," Linda said again, and he felt her hand squeezing him more tightly. "No, no!" But the man took hold of one of his arms, and it hurt. He screamed. The man put up his other hand and lifted him up. Linda was still holding him, still saying, "No, no." The man said something short and angry, and suddenly her hands were gone. "Linda, Linda." He kicked and wriggled; but the man carried him across to the door, opened it, put him down on the floor in the middle of the other room, and went away, shutting the door behind him. He got up, he ran to the door. Standing on tiptoe he could just reach the big wooden latch. He lifted it and pushed; but the door wouldn't open. "Linda," he shouted. She didn't answer.
[…] He hated Popé. He hated them all – all the men who came to see Linda. (8.9-11)
Here we get our first glimpses of John's rage at Linda's promiscuity, which is probably related to his later anger at Lenina for being just promiscuous. This is Freudian, big time.