When I was teaching, back in the 1970s and 1980s, it was a serious disciplinary offence for any member of staff to use the word 'coloured' with reference to race, potentially leading to dismissal.
The use of that term by any pupil was also a matter that was regarded as being extremely serious, involving referrals to senior staff, probable disciplinary action and the possible involvement of parents. So your mother appears to be at least 40 years behind much of the rest of society!
I do sometimes have to stop myself using terms I picked up in my childhood though, such as the deeply offensive 'half-caste' for a person of mixed race. Like your mother, I'm (hopefully) not racist per se, but old habits do die hard!