Previous studies demonstrate that lexical coding of colour influences categorical perception of colour, such that participants are more likely to rate two colours to be more similar if they belong to the same linguistic category (Roberson et al., 2000, 2005). Recent work shows changes in Greek–English bilinguals' perception of within and cross-category stimulus pairs as a function of the availability of the relevant colour terms in semantic memory, and the amount of time spent in the L2-speaking country (Athanasopoulos, 2009). The present paper extends Athanasopoulos' (2009) investigation by looking at cognitive processing of colour in Japanese–English bilinguals. Like Greek, Japanese contrasts with English in that it has an additional monolexemic term for ‘light blue’ (mizuiro). The aim of the paper is to examine to what degree linguistic and extralinguistic variables modulate Japanese–English bilinguals' sensitivity to the blue/light blue distinction. Results showed that those bilinguals who used English more frequently distinguished blue and light blue stimulus pairs less well than those who used Japanese more frequently. These results suggest that bilingual cognition may be dynamic and flexible, as the degree to which it resembles that of either monolingual norm is, in this case, fundamentally a matter of frequency of language use.