Why Gallifrey's Sky Is Red

It seems that one of the most stunning optical qualities of Gallifrey were its two suns orbiting the Shining World of the Seventh System in a red-orange sky. 

Red...

And even though 'Doctor Who' does not feature many episodes which are set on the Doctor's home planet, or show glimpses of it, when it does, its skies are not always red ("The Five Doctors" or more recently "The Name of the Doctor"). 

... and not so red.

So, did the big guys responsible for the show get something wrong (again)? Not necessarily. Because, surprisingly, this time there may be a physical explanation behind it.

Now, when our sun sets or rises, our skies are usually tinted red too. This is because at sunset the light hits earth at a different angle which makes it travel longer distance than at noon. And the shorter wavelengths of the light (green and blue) become scattered on the way. It's only the longer wavelengths (red, pink, orange) which manage to make the long way. But to get the best effect it also takes a lot of particles (e.g. clouds, oxygen) in the sky which allows the light-waves to bounce off and to become visible.

Gallifrey has two suns and if one of them is setting or rising the air becomes flooded with long reddish wavelengths and the skies turn red. However, when none of them is the sky is of an ordinary blue.