10 Unnecessary Doctor Who Details You Need To Know

In the RTD1 era, Doctor Who’s brand strategy was more on-point than ever before.

This extended to the show itself, with an unprecedented level of continuity between the designs of the TARDIS and the sonic screwdriver. But an even niftier detail that you might not have noticed is that there was also a colour-coding system for the time vortex seen in various episodes.

The rule was simple: a blue vortex meant that the TARDIS was travelling backwards in time, while a red vortex meant it was travelling forwards.

Every TARDIS vortex shot in Series 1-4 abides by this principle. In Series 1, for instance, a blue vortex is used to indicate the historical settings of The Unquiet Dead and The Empty Child. Meanwhile, one of the most memorable uses of the red vortex is in the pre-titles scene of Utopia, where the TARDIS – complete with stowaway Captain Jack – hurtles towards the year 100 trillion.

Of course, both variants also appear in the title sequence at the start of each episode, with the TARDIS initially travelling through a blue vortex (aka the past), then switching to a red one (aka the future).

This colour change is never remarked upon in the show, so it’s not something that many people will have noticed. But once you know it’s there, you’ll never unsee it!