That's because throughout the show, they have used this shade in scenes where tensions mount. Or have you noticed that in The Matrix, the majority of the movie is green?
These subtle, yet noticeable, details help to create a certain mood which the director is trying to convey. This is why is horror movies, you will see lots of blue coloring, due to the melancholy nature of the color, or grey in post apocalyptic movies. The use of color is really just as important as any other aspect in creating the mood you are going for, so going forward it's always a good idea to consider it. After all, a regular scene can become something special when more meaning is put into it.