Genesis 25:29–30 (JPS):
And Jacob sod pottage; and Esau came in from the field, and he was faint. And Esau said to Jacob: 'Let me swallow, I pray thee, some of this red, red pottage; for I am faint.' Therefore was his name called Edom.
The Hebrew version, too, has Esau saying red twice ("הָאָדֹם הָאָדֹם"), implying that the lentil pottage was very red, or at least that the color was very important - see other occurrences of repetition: Genesis 22:11 compared with Genesis 22:1, 2 Kings 4:19 and 2 Samuel 19:1 (in 2Sam too the English translations omit or miss the strict repetition).
But red lentils lose their color when cooked, and tomatoes and bell peppers weren't around, being from the Americas.
Is there some lore about the content of the stew that Jacob cooked?