The Unicorn theme is played when Rosella encounters the wild unicorn in the fields by the shores of Tamir. The song was composed by William Goldstein and uses uses a bright brass melody with string harmony.
King's Quest IV: The Perils of Rosella (DOS)
Five different types of output were designed for the DOS release, each output corresponds to a different group of devices, the Roland, Yamaha, OPL2, 3 Voice, and PC Speaker.
The optimal MT-32 output uses a bright brass melody and a string harmony. The OPL2 version uses a much warmer sounding brass for the melody. The 3 Voice isn't capable of keeping any instrument timbres, but keeps the melody and harmony intact. The PC Speaker version is only able to play the melody, and without volume decay it sounds quite awful.
The file is sound.032 in the resource files, and it does not loop.
King's Quest IV: The Perils of Rosella (A2GS)
The Apple IIGS port plays the song on the built-in ES5503 audio chip.
King's Quest IV: The Perils of Rosella (AMI)
The Amiga port plays the song on the built-in 8364 audio chip.
King's Quest IV: The Perils of Rosella (AST)
The Atari ST port included at least two types of output, one for Roland devices and one for the system's built-in YM2149 audio chip. Since the Roland output is the same as the DOS release, it will not be recorded.
The Apple II port does contain music, but this song was excluded to conserve space.