The color master tape of this episode was wiped by the BBC in the 1970s and the BBC only held a 16mm black and white telerecording. The episode remained only in black in white until the 1990s, when the color signal from a domestic NTSC recording and the black and white telerecording were used to create a new color master on D3 digital tape.
This episode was watched by 7.2 million viewers on its original transmission.
Derek Pollitt who has a tiny role in this has acted in both the Black and White and color era of Doctor Who.
The Doctor claims to be "several thousand years" old, which is at odds with nearly every other indication of the Doctor's age.