Terror exists in colour, but in the same reconstructed-from-two-sources form
I distinctly remember seeing a full color version at some point. I think it was sold on VHS tape. Is this the reconstructed version you are talking about?
It is, yes. The two sources are a black and white telecine (film print) copy, with better resolution, and an off-air colour recording made by a Canadian fan from an early US transmission, the flaws in this being that it's on NTSC Betamax which was then copied and converted to PAL um-matic for another fan (Ian Levine, to be precise). So that copy is a little ropey, but it could provide the colour info to turn the B&W version into the colour version that's been released, thanks to computer trickery that was frankly miraculous for the time.
16 years later, redoing it will produce a far better version, which has been done for the other stories where the colour version comes from these sources: The Daemons was, I believe, redone for a BBC4 transmission a couple of years ago, and The Silurians was redone for a 1999 BBC2 repeat, and then again for the DVD release two years back.
Ambassadors of Death has also been partly recreated using the same method, but the weather was bad on the day the Canadian fan taped it, so the colour sometimes drops out of his recordings, unfortunately.