Quoting Colin Farrell:
The film’s split into two hemispheres – one being the Colony and the other being the United Federation Of Britain.
So over in the Colony, which is mainly full of proletariat, the weather’s more symbolic of the more downtrodden existence that the people there have. So it’s always dark and rainy.
And then in the UFB, which is very unlike Britain, the skies are sunny and clear and things are a little bit more optimistic.