I remember when I first played it, I didn't know if I'd ever get used to it. The first mission had the super dark and drab weather and I thought it sucked ass. I kind of like it now. I agree the world could be more colorful, but it really does seem to capture the "grunginess" of NYC.
I sunk over 100 hours into it and I think it's a great game but I think it was still a poor design choice. They're just falling in rank and file with the rest of AAA game titles produced today but I think if they made the game really colorful they would be really surprised and like it, and so would their audience. I mean a little gray or brown or black is fine but even the trees leaves looked dead,
like they had a layer of brown film over them that wouldn't come off no matter how much it rained.
The only place you see gray like that is former Soviet republics, and many of them have
more color because they locals painted their buildings bright colors. If you go into a large city today it's not a bunch of gray squares like you see in the screenshot there with the flying car (which is awesome). The buildings are brown, orange, gray, black, bright white, pink, and blue. Many are covered in glass and reflect the sky, so it literally looks like the building is made of clouds.
If you look at the fan made mods that added more color, they all look stunning and 100 times better than the original game, hands down.
On the other hand, Alderny is a stunning replica of New Jersey, which really does look that dead (when you're in the city anyway).