Tyrannnical action by the BBC?
Free the Colourised 2!!
I think what this would come down to is an issue of cost effectiveness. Considering they won't even produce any more animated recreations of lost episodes, I can't see them spending money colourising ones they can just as easily sell as they are.
And TOS is a poor comparison. Star Trek was filmed in colour, Who was not, and whilst many of the sets/cosumes were coloured (see Zoe's catsuit for further details) many of them were actually just varying shades of grey because the show was designed to be filmed in B&W.
I think another interesting point is that in many cases whoever did this would in effect be imposing their own colour pallate onto the show. Take Zoe's catsuit (I'm not obsessed!) It's actually purple, but would the producers have made it purple if the show was intended in colour? Or was it chosen because it looked good in black and white, or just because it was the only colour available. So do you colour it purple (which may or may not have been the original intent) or do you make a choice based on what colour you think it should be?