Here we report the results of a brief experiment investigating the role of attention in mediating contextual effects on synesthetic experiences. Specifically, we examine a grapheme-color synesthete for whom the grapheme letter 'O' and number '0' are associated with two very different colors. We presented the grapheme '0' in an array of graphemes that provided ambiguous contextual cues, such that the same grapheme could be perceived either as the number '0' or as the letter 'O'. We find that an attentional cue that draws attention to one or the other of the contexts biases the perceived synesthetic color of the '0' grapheme to that associated with the cued context. This is true even when the physical color of the grapheme corresponds to the un-cued context.