When I initially picked the color scheme for digester, I wanted to find something I personally like. I knew the brownish orange was an unconventional pick, but I wanted to create something unique.
In the meantime I both received complaints from users that the color scheme is outright ugly (or a kinder form of the same message) and I read up on color theory. Blue is a natural choice for digester, because it is the color of calmness.
Is it a coincidence that both Twitter and Facebook picked blue as well? Do they want to signal calmness with that? To me, both of them are quite the opposite: attention grabbing and interrupting!