When the Torah commands that each tribe camp under its own standard — every man by his own banner, with the ensigns of their fathers' house (Numbers 2:2) — the Rabbis were curious. What did those banners actually look like?
The Midrash (Bamidbar Rabbah 2) answers that the twelve princes of Israel chose the colors for their flags from the twelve stones on the breastplate of Aaron the High Priest. Each tribe's stone gave its banner its hue. And each added an emblem from the blessings its founder had received.
Reuben, the firstborn, flew a red banner with mandrakes on it — the plant Reuben once brought to his mother Leah. Issachar flew a deep blue banner showing the sun and moon, because Jacob had blessed his tribe with wisdom in reading the seasons. Naphtali chose an olive tree, drawing on Jacob's blessing — Out of Asher his bread shall be rich (Genesis 49:20) — which the Midrash reads as olives running with oil. Judah flew a lion. Benjamin a wolf. Joseph an ox. Simeon the walled city of Shechem. Every tribe carried its father's last words on a pole above its tents.
From this tradition, the Rabbis add, later princes of other nations learned the art of heraldry. The whole grammar of distinguishing flags and coats of arms — colors, emblems, symbols that say who you are and where you came from — begins, in the Midrash's telling, with the twelve tribes of Israel in the wilderness.
The teaching, preserved in the 1901 anthology Hebraic Literature, is a quiet point about identity. The Rabbis did not imagine Israel as twelve tribes dissolved into one amorphous crowd. Each tribe kept its color, its emblem, its memory of a particular blessing. Unity in Judaism has never meant sameness. It means twelve different flags marching in the same direction.