You haven't really answered both parts of the question. I understand why the word coloured is deemed to be unacceptable but that doesn't explain why 'people of colour' is acceptable. As I see it, either both are acceptable or both are unacceptable. Can't really have it both ways.
"Historian Dr Joe Street, of Northumbria University, says the term “people of colour emphasises the peoplehood” while “coloured” is “depersonalising”." https://inews.co.uk/news/uk/coloured-offensive-why-term-greg-clarke-fa-chairman-what-say-comments-resigned-756234
Not quite sure I understand that explanation - hopefully there are better ones?