It looks like an aesthetic decision. All digital footage for TV or film is color graded after it's shot, so when you're watching professional material, the 'look' is never going to appear how the cameras captured it. In this new season, the blacks are crushed, colors muted in outdoors shots, and the whole thing has a slight blue tint to it. It's definitely intentional, and I personally thought it looked pretty good, very cinematic. I'm not British, but here's caps from the original feed: (Check out that woman's coat on the left; there's no detail in it at all. They've definitely crushed the darks way down.) The color palette appears to get less saturated and colder as the episode goes on, which I hadn't noticed before. Maybe to enhance a sense of a looming threat?