Del Shannon's "Two Silhouettes"

Last month, I learned the chords for Del Shannon's "Two Silhouettes" and noticed a feature with an accidental.

First of all, here are the chords (with the disclaimer that, as always, I might have something wrong):

Intro
|: C major | Bb major :|

First verse
C major | A minor
F major | C major | G major
C major
F major | D major
|: C major | A minor :|
C major | G major | C major

Link
|: C major | Bb major :|

Second verse
C major | A minor
F major | C major | G major
C major
F major | D major
|: C major | A minor :|
C major | G major | C major
F major | C major

Bridge
F major | C major
F major | G major | C major
F major
G major

Third verse
C major | A minor
F major | C major | G major
C major
F major | D major
|: C major | A minor :|
C major | G major | C major

Tag
|: C major | Bb major :|

The song is in C major, and - aside from the Bb major in the instrumental sections - the only chord with an accidental note is D major (with an F#).  In two of the verses, the lyrics above this chord describe a change.  In the first verse, the line there is "And all the rain seemed to turn to tears" and in the third verse, "I know things will never be the same."  That F# accidental helps to musically portray the "turn" and not being "the same."  One of the voices in the backing vocals even goes from an F natural to an F# during that line, emphasizing the accidental.