ATV Production without the colour?

I notice from the Tiswas credits added to TV Ark today that particular 1981 edition carried an endboard which just read 'ATV Production' - the colour line had been removed. Was there ever a change of policy at ATV to remove it (I assume there would have been plans in place to get rid of it if Central wasn't just around the corner), was it just confined to particular programmes, or is it a result of re-editing the programme masters? (I've seen the masters re-edited to remove 'Colour' from early colour programmes which now only exist in a B/W format, but I can't see why they'd do it to a 1981 Tiswas).

What an oddity! I have not seen one like that before, as that type usually looks like this, I too am intrigued as to why it is absent!

http://www.rp-networkservices.com/tvforum/uploads/atvproduction.jpg
Here is a screenshot from the clip. Looking at it more closely now, as it's a keyed slide and you can still see the correct image where 'Colour' would normally be (the image continues to move too, so it's not been done by any freezeframe techniques), I can only assume it was made that way and isn't the result of Polygram titting about with it.

Anyone know why this would have been done? I know the frontcap still carried the 'In Colour' line until the bitter end, so it surely wasn't a policy decision to remove it from the endcap but not the frontcap?

It's a small point I know, but this one has got me intrigued.

It's from a geniune 1981 betamax videotape recording. The blank space is where the word 'TISWAS' would normally have appeared.

BTW - this kind of query is what the TV ARK Forum is for!