"From that red, red stuff" (Genesis 25:30). Rabbi Yohanan said: [Esau is condemned] from himself and from his patron. Resh Lakish said: from himself and from those like him. He is Edom [the Red One]: "And the first came out ruddy" (above, verse 25) — he himself was red; his stew was red, "Let me gulp down some of that red stuff"; his land is red, "to the land of Seir, the field of Edom" (Genesis 32:4); his warriors are red, "the shield of his mighty men is made red" (Nahum 2:4); his garment is red, "valiant men in scarlet." Red [Edom] will exact punishment from him: "My beloved is dazzling and ruddy" (Song of Songs 5:10) — clothed in red, "Why is Your apparel red?" [the LORD comes in red-stained garments to judge Edom].
Red From Crown to Garment and the Red Reckoning of Edom
Yalkut Shimoni on Torah 111:1
מִן הָאָדֹם הָאָדֹם הַזֶּה, רַבִּי יוֹחָנָן אָמַר, מִנֵּיהּ וּמִן פִּטְרוֹנָהּ וְרֵישׁ לָקִישׁ אָמַר, מִנֵּיהּ וּמִן דְכַּוָותֵיה הוּא אָדוֹם (לעיל פסוק כה) "וַיֵצֵא הָרִאשׁוֹן אַדְמוֹנִי", תַּבְשִׁילוֹ אָדוֹם, הַלְעִיטֵנִי נָא מִן הָאָדֹם, אַרְצוֹ אֲדֻמָּה (בראשית לב, ד) "אַרְצָה שֵׂעִיר שְׂדֵה אֱדוֹם", גִּבּוֹרָיו אֲדֻמִּים (נחום ב, ד) "מָגֵן גִבּוֹרֵיהוּ מְאָדָּם", לְבוּשׁוֹ אֲדֻמִּים, "אַנְשֵׁי חַיִל מְתֻלָּעִים" יִפָּרַע מִמֶּנּוּ אָדוֹם (שיר השירים ה, ו) דּוֹדִי צַח וְאָדוֹם בִּלְבוּשׁ אָדוֹם "מַדּוּעַ אָדוֹם לִלְבוּשֶׁךָ".