This study reports three cases of synaesthesia who experience colors in response to written musical notation, graphemes and heard music. The synaesthetes show Stroop-like interference when asked to name the colour of graphemes but not for written musical notes. However, reliable interference is found in two further studies that require deeper processing of the musical notation (namely playing music from colored notation, and naming the synaesthetic color of the notes whilst suppressing the veridical color). This is the first empirical demonstration of synaesthesia for musical notation. The fact that synaesthetic color influences music playing/reading (a sensory-motor transformation) but not verbal color naming suggests that synaesthetic Stroop effects can arise from processing the meaning of a stimulus and not just as a result of verbal response interference. However, it is likely that the color associations themselves have a developmental origin in the names assigned to them. In all three cases, the colors of the written notes are related to the graphemes that arbitrarily denote them (e.g., 'A' may be “red” both as a letter and when written in musical notation). The results suggest that synaesthetic associations may migrate from one representational format (e.g., graphemes) to another (e.g., musical notation).