I'm having problem coloring notes

[Xiaoyu Ding]

Hi,

I saw from your doc that I can color notes using:
     \override NoteHead #'color = #red
     c4 c
     \override Stem #'color = #blue
     e

But when I try to color a note using:
    <bes  
    \override NoteHead #'color = #blue 
    g 
    \override NoteHead #'color = #black>4 |

I got an error:
    error: syntax error, unexpected \override, expecting DRUM_PITCH or 
NOTENAME_PITCH or '>'

Is this because that I'm trying to color a note within a chord?  Is that 
allowed?  If not, is there a way to color (or change the look of) one note 
within a chord/phrase, etc.?

Thanks!

Xiaoyu