The intro for Dr Who shows the tardis flying through the time vortex that takes one of two shades, sometimes transitioning between the two:
The Vortex generally had two different colours, red and blue. Red generally indicated forward time travel and blue indicated travel to the past.
~Dr Who Wikia
And confirmation elsewhere:
In the new series (revived in 2005), the direction of the TARDIS's time travel through the vortex can be discerned from the surrounding colours: blue for travelling into the past and red for travelling into the future, most likely inspired by the Doppler effect.
~Wikipedia article on the Time Voretex
In the last two episodes I've seen green and red flashes of lightning in the 'blue section', a transition to a fiery red version of the vortex. I know this lightning is new from season/series (DaA) 5/6 but now it seems it no longer 'functions' the way it used to.
Is that correct? Why do we have the lightning? Does the colour still reflect the direction in time the Doctor travels?