Now I sure wouldn't want to write an effect by hand having ten layers, four rotations and eight clips per syllable... anyway...
On the suject, the question is actually whether the idea is that the syllables should first start fading out after their entire duration has passed, or they should start fading out while still being highlighted. The effect obtained by leaving it as-is and just applying my fix also gives a quite interesting effect, especially if you let color1 and color2 fade towards the same.
(Oh yes, and I prefer \kf for readability, IMO \k and \K just look too similar
)