Russian has two separate words for blue — light blue and dark blue are different colours

In Russian, 'goluboy' (light blue) and 'siniy' (dark blue) are as distinct as 'green' and 'blue' are in English. A landmark MIT study found that Russian speakers are measurably faster at distinguishing shades of blue than English speakers, specifically across the goluboy/siniy boundary. Language, it turns out, genuinely changes how fast you perceive colour.

Source: Winawer et al., 'Russian blues reveal effects of language on color discrimination', PNAS (2007)