The Jewish Action article mentioned by @dov (thank you) contains the following paragraph:
The earliest mention of the ketonet passim being a variegated garment
dates back to the third-century bce Greek Septuagint, which translates
it as χιτῶνα ποικίλον (poikilos)—a cloak of various colors. (In II
Samuel it translates the same word differently: karpótos.) Following
the Septuagint, the fourth-century Latin Vulgate translates ketonet
passim as “tunicam polymitam”—a tunic woven with many threads, usually
taken to mean different colored threads. The early seventeenth-century
English King James Bible calls it a “coat of many colours.” Possibly
based on this, the once standard Jewish English translation, the 1917
Jewish Publication Society (JPS) Tanakh, calls it “a coat of many
colors.” Some traditional commentaries adopted this interpretation.
The influential eleventh-century Hebrew grammarian Jonah ibn Janach
(Sefer HaShorashim, entry “pas” [p. 405]) assumes “passim” is the
plural of “pas,” and based on Daniel and the Targum to Kings, “pas” is
a handbreadth; thus, the ketonet passim was a silk garment in which
each handspan was a different color. Radak (1160-1235; Provence),
based on Daniel, derives that the garment was made of stripes of
various colors. Ralbag (II Samuel 13:18) says that each handspan of
the garment was a different color, and it included many colors.
So the well-known commentators who subscribe to the colours idea are the Radak and the Ralbag.