I have a hazy memory from the late 1960s/early 1970s of reading an ongoing story, I think on on the back page of a British comic, of a world where everything had been turned black and white. The main thing I remember is the concluding episode where more and more was in colour in each panel which looked pretty cool to an 8 or 9 year old.

Trouble is I can't remember the name of the the series or which comic. It might have been in Look and Learn but I'm not sure. Can anyone else remember it?

Blimey I'm way before that period tbh BUT it might have been Alfred E Newman..."MAD" comic...? in my days we WERE just in black and white...
My dad bought a black and white DOG... then just 'cos the licence was cheaper.....

A long shot but could it have been "Playhour"? This comic for very young kids had a beautifully painted strip starring a character called Gulliver Guinea Pig who had at least one adventure in a b & w world where he touched things and they became coloured.

That sounds like it might be it. Thanks so much. I'll go and investigate Gulliver further!

Try www.26pigs.com. It had info on lots of old UK comics.