In the discussion regarding this verse in the Babylonian Talmud (Sanhedrin 98a), a story is told of the Persian king Shevor, who says to Samuel, one of the Amoraim, "You say that the Messiah will come on a donkey; I will send him the riding horse that I have."
In response to the ridicule of the king, Samuel answers, "Do you have a horse with one thousand colors like the donkey of the Messiah?
In Israel, the phrase "the Messiah's Donkey" can also refer to the controversial political-religious doctrine ascribed to the teachings of Avraham Yitzhak Kook which claims that secular Jews, which represent the material world, are an instrument in the hands of God whose purpose it was to establish the State of Israel and begin the process of redemption, but upon its establishment they would be required to step aside and allow the Religious-Haredi public to govern the state.
A book called The Messiah's Donkey, which focuses on this issue, was published in 1998 by Seffi Rachlevsky and caused widespread controversy among the Jewish public; according to Hassidic teaching the donkey is a symbol of the fact that the Messiah and Messianic age will not oppose the material world, but rather control it for sacred purposes.
The uncle sidestepped the point by remarking: "when the Messiah came, there would be utter pandemonium and the Jews would jump on the first donkey that came their way without checking out its sect!