1)
Why does it say "Adom li'Lvushecha"?
1.
Radak: The prefix Lamed in li'Lvushecha is [extra], like "Hargu l'Avner" (Shmuel II, 3:30), "veha'Shelishi l'Avshalom" (Divrei ha'Yamim I, 3:2). Hashem is depicted as a Gibor taking vengeance on his enemies. His clothes are red from blood.
2.
Radak citing Targum Yonasan: Why are these mountains red from blood?
3.
Malbim: He came primarily in Levush to make His Malchus and Elokus apparent. They did not recognize it, so His Levush became red to take vengeance over this. Via this, also his others garments became red.
