Who needs colour, anyway? Killzone 2 ignores your TV's ability to display a zillion colours at the same time, and still manages to look nice.
They look to have been taken from the same outdoor battleground as levels we've previously played through, and you can read all about that here.
You never know, this is an alien planet - maybe later stages are set in a colourful toy land where environments are made of sweets and chocolate and the sky is full of rainbows.