I've got dark red hair, DD's a bright strawberry blonde, DS has a brilliant red curly afro - up till puberty, he looked like a renaissance cherub (and hated being reminded of it).
I was bullied as a child because of it. When both DC's were babies and their hair came through red, I lost count of the "jokey" comments from "friends".
On facebook: "Love the picture - you can't tell she's ginger in that one"
"Oh, what a shame - I really thought your DS's hair would grow out blonde"
"Wow, your DS is walking early, mine's really late but at least she isn't ginger"
"my DD's a little monster. Only way it could be worse is if she was as ginger as your DD"
It was a constant thing from nearly everyone.
One day on a walk, they were shoving each other and ended up throwing themselves in a heap at the feet of a stranger walking nearby. I hauled them up by the collars, told them off for being a nuisance and apologised to the guy they'd nearly hit.
He said "oh, don't worry about it - they're ginger, that's punishment enough".
Even my bff at the time would constantly joke about how ginger hair was the worst thing that could happen to a kid and kept asking me when I was getting mine adopted.
Once you've heard them all repeatedly over many years, you sometimes get a sense of humour failure over a comment that really seems unnecessary. I have had so many occasions where I've replied something along the lines of "can you not say things like that in front of them, they're already being bullied at school because of their hair"
at which point, the person who's literally insulting your kids genetic makeup gets huffy and pissed off because "you know I would never actually say that seriously - it's just a joke, for god's sake."
One school mum used to tell me that I should get them adopted but I'd have to dye their hair first otherwise no-one would take them, leading onto things like "you'll have to take them to 'disneyworld' and drive away when they get out of the car".
Honestly - she said that. But obviously laughed and would go "oh, you know I don't mean it". She stopped talking to me when I came out with a couple of blonde jokes that she thought was absolutely disgusting because it'd damage her daughter's self-esteem.
Not my proudest moment, but I was pissed off and I made sure it wasn't in front of her child. On the plus side, I never had to speak to her again, so... totally worth it.
I try not to get defensive but some of the comments from people saying "surely nobody mocks ginger hair nowadays" implies we're making it up and it's not really a problem.
If this is your mindset, be grateful that you don't have to deal with strangers insulting your children and it has so little impact on your day-to-day that you don't think it happens very often. I frequently wish that we had the luxury of thinking "ginger insults aren't a thing any more".