wow, thats a lot of things that talk about redheads being the illegitimate offspring. Good thing my dad and uncles had red hair or else my mom would have been in trouble.
That red-head kid in my avatar is a quarter Korean. And until well after he arrived I was dying my hair blond and had NO idea that I would find some red if I let my hair go the way it wanted to go.
When he was out, and I'm not exaggerating when I say he had absolute orange, Ronald McDonald hair, we were all a mite surprised! Hubby's sister's kids have basically the same mix of backgrounds (her kids' father and I are the same basic western European mix as each other), and her kids look more Korean than she does (and she and my husband look disturbingly alike, LOL). We weren't expecting that!
As we talked to family members, it turned out that my grandfather, from whom I inherited my curls, had auburn hair (he died in his 50s while I was still a fetus and all pictures of him are in black/white), and hubby's father's aunts both had red hair, but they were much older than FIL, and FIL was in his 70s when DS arrived, so we definitely had never known that they had red hair.
I guess my dad said "uhoh" when he saw DS's picture.
Since DS was a honeymoon baby, I'm a little disturbed at what my dad thinks of my morals!
Anyway, I've always heard the phrase as a two-fold thing. Red hair is recessive, not everyone has it (though I've seen more red headed babies and toddlers in the last few years than I've seen in adults my whole life, my week in Ireland excepting), so you're unusual. Plus, in some cultures, it was seen as a sign of witchcraft, during times that witchcraft was seen to be very very bad. And stepkids, well, look at Cinderella. Her stepmom surely didn't treat her very nicely! So you're already unusual, and then you're around people who don't necessarily care for you as you're own...boy howdy are you in for trouble!
(so sayeth a stepchild three times over who, it turns out, has reddish hair when she doesn't force it to be blondish!)
I'm able to laugh at it now, but I was highly offended back then.
I have only heard one expression..when someone is being ignored or shunned, they are being threated "like a red-headed stepchild at a family reunion."
And he was not Dutch. No one remembers him to tell us what he looked like. I've often wondered if he was born with RED hair and was named Orange because of that, since his daughter had auburn hair. Why else would a person name a child Orange? This would have been the mid-1800s. I don't think it was such a fashionable a name then that you'd be driven to name your child that???? 
It was so bizarre!
I honestly don't know where anyone got that.
