I've been asked if I was a childminder lots of times in the past as well and that's because I have 5DC,it's never offended me it made me laugh that so many people presume that if you have over 2DC they can't possibly be all your's.
The lady that presumed that my Irish husband(now ex husband)couldn't be my sons Father because my son has lovely golden skin,very dark almond shaped eyes and black hair(he looks far more like me than his Father)wasn't being racist and it didn't offend me although it could have caused me problems as my ex husband was an abusive bastard!
But did I,would I have blamed her if he'd kicked of at me no of course I wouldn't she wasn't to know!
Being called dirty,your ancestors having been hounded and gassed because of who they were,being attacked physically,being treated unfairly because of who you are,where your ancestors are from,where your from,obscenities and vile names being said about you,offensive jokes at your expense because of the way you look,your herritage,your beliefs,the way you talk that's all racism.
And that's something all of my family have been raised for generations to never except even if that means stepping in and protecting someone we don't know.
What's happening in America is Racism,not someone asking a question and making a mistake,unless they're saying it in a nasty way or are being an arse I wouldn't call it racism.
Being as you talk about racism OP I'm surprised you said the word coloured my friends would call you racist they can't stand that and I agree with them!