Wikipedia elaborou muito bem:
Another recurring image related to the spirit of the film is that of elderly people recycling bottles: In Blue, an old woman in Paris is recycling bottles and Julie does not notice her (in the spirit of freedom), in White, an old man also in Paris is trying to recycle a bottle but cannot reach the container and Karol looks at him with a sinister grin on his face (in the spirit of equality) and in Red an old woman cannot reach the hole of the container and Valentine helps her (in the spirit of fraternity).
Portanto, este tema recorrente abrange o lema da República Francesa: liberdade, igualdade, fraternidade .