I remember this discussion over at Livejournal before about the meaning of hair colour in superhero comics where in the case with the womenfolk, blonde hair often immediate denotes beauty and red-haired women are either dangerous or dangerously fun with the exception of Barbara Gordon at the time. Like how there’s a tendency for cartoonists to make the daughters more closely resemble their mothers, with the exception of Mayday Parker who resembled her father more. Right down to the similarly dark hair and her outfit being nearly identical to his, instead of being a feminised or skimpier version of the male counterpart’s outfit. As it is with Batgirl and Batwoman to Batman, Supergirl to Superman or Hawkgirl to Hawkman,
In the case with Rachel Summers, the daughter of Scott Summers and Jean Grey, considering that her maternal grandmother (Elaine Grey) is blonde or perhaps was blonde, and that Scott’s own brother Alex is blond himself, which should make pedantic sense that Rachel should’ve turned out blonde herself. But I suspect giving her red hair is meant to communicate that she’s practically her mother’s doppelganger, which is particularly true over the years. To the point of taking on one of her mother’s former nom de plume Marvel Girl for a long while, dressing up very much like her from time to time that the biggest visual difference between the two is that Rachel often has shorter hair. If she had been blonde, this wouldn’t be the case.
Maybe not to the same extent that I’m proposing but easier to tell apart in terms of appearance alone, though it’s possible some cartoonist briefly gave her blonde hair by accident before, that she may not have been made into a Jean Grey doppelganger so often if this was the case. It’s very obvious that since from the start that Rachel was and still is meant to be a Jean Grey doppelganger, she doesn’t just have her mother’s abilities and hair colour, she also sometimes dresses up like her and even share the same nom de plume together. She’s very derivative of her mother in ways her brother Cable isn’t, despite sharing the same parents and abilities together. This says a lot about the way she’s written over the years.
That’s not to say I hate her as a character, but there’s no mistaking that she’s very similar to Jean Grey in many, if not most, regards. Not necessarily entirely identical but similar enough to act as an adequate understudy for her whenever Mummy Jean’s away or something, which really hurt whatever claims to uniqueness Rachel herself may have had. The way she’s written over the years should tell you that there’s a tendency for writers to treat her like a Jean Grey doppelganger, not just in abilities and hair colour, but also how and why she even dresses up like her from time to time.
This may not be unique to Jean Grey herself as Emma Frost might have hers with the Stepford Cuckoos, but with other characters it’s not exactly, particularly nor wholly the case. Nightcrawler is Mystique’s son and shares the same blue skin as hers, but his ability is very different from hers so he’s never going to be his mum’s doppelganger. Vanora is Rahne Sinclair’s daughter but while both women have the same ability (turning into wolves), she looks and acts differently from her as to not be her doppelganger either*. Theresa Cassidy bears similarities to her father Sean but she’s more of his female counterpart, rather than be an outright doppelganger for him the way Rachel is to her mum.
When she’s been shown to dress much like her own mum in a consistent number of instances, even if it may not’ve been especially frequent, take on her mum’s codenames and even wore an outfit similar to hers as Marvel Girl for a time in the 2000s, then she really is her mother’s doppelganger and far more often than what Vanora is to Rahne Sinclair. She’s often her own mother’s understudy in a way the other X-Progeny aren’t to their own parents, the latter aren’t to the same extent that she is to Jean Grey really. So it’s inevitable that she’s going to be compared to her, since she is the prototype for the sort of character Rachel grew into. Assuming if she may’ve been more different at the conceptual stage.
But I suspect that writers frequently turning her into her mother’s doppelganger and understudy undermined their ability to make her actually stand out from her in some other way, that it’s going to be real tricky into not making her Jean-lite. Whatever attempts at making her stand out more from her mum tend to be short-lived, since her time as Mother Askani was undone by the time she reappeared as a young woman again. At other times, they’re often not well-thought. That’s not to say she sucks as a whole but that it’s harder making her stand out from Jean, when she’s so often turned by writers into her understudy and doppelganger.
*I could be wrong in here as she may’ve been her mother’s doppelganger in a sense (as she could take on any wolf form), though not as often as Rachel is to Jean, which is saying since she doesn’t make any further appearances since then.