Rebecca De Mornay pulled a textbook example, in the 1990s classic The Hand That Rocks The Cradle, as an ice-cold, vengeful but seemingly sweet and inoffensive au pair out for the blood of the woman who got her obstetrician husband charged with sexually molesting his patients (by way of her family).
In the episode "The Power of Three Blondes" is about three criminal witches, named the Stillman Sisters, who are all blondes, and their characterization is largely built around their blondness. They are an Evil Counterpart to the Halliwell Sisters, who are all brunettes, though Paige was actually strawberry blonde at that point. Only one of the witches actually fit the trope as the other two were more Dumb Blondes who happened to be evil.
This is a rather common trope in Telenovelas, or Spanish-language Soap Operas. It's a bit complicated to explain, but it seems to come from the fact that blondes in Latin America tend to come from richer families.
At the beginning every main blond character on Glee is evil: Sue, the glee club's arch-enemy
Will's wife, Terri, who doubles as a Dumb Blonde
And Alpha Bitch, Quinn.
Even Brittany, who is such a ditz that it's a miracle she can compose sentences, is an Ineffectual Sympathetic Villain as a spy for Sue.
Legend of the Seeker, particularly in the second season, contrasts blond, morally ambiguous villain/antihero Cara with pure, moralistic, dark-haired Kahlan. This is also at least a partial subversion, because it turns out that Cara is a tragic figure of corrupted innocence while Kahlan becomes something of an uptight bitch.
The girl with the curls is the real vampire. I found that out when I was in the chorus. It was the blond cutie that did all the damage to the front row.
— Nita Naldi (dark-haired actress typecast as a villainess)
This is the female version of Blond Guys are Evil. It sometimes overlaps with Evil Is Sexy.
These are blondes from societies where the hair color occurs naturally. The characterization differs when the blond hair is a clue that the character is an evil foreigner.
Often contrasted with a dark-haired heroine — as the Femme Fatale or Alpha Bitch compared to the Girl Next Door, The Vamp rather than the Distressed Damsel, the City Mouse rather than the Country Mouse.
She is not too likely to be the Dumb Blonde, but can be, with her plotting being run more on animal cunning than cleverness, and many evil blondes have exploited the Dumb Blonde stereotype.
This hair color can be dyed and often is. In the City Mouse, this is part of the luxuries of the city. For the Femme Fatale or The Vamp, it is a calculated part of her scheming. And it can, for any evil blonde, be a symbol of her deception or her lack of simplicity. Indeed, this may drive this trope's interchange with Hair of Gold, a deeply Cyclic Trope.
When blondes are natural, blondness does correlate with youth (and, presumably, innocence) and so is attractive. Women therefore dye their hair blond. But after a critical mass of blondes have dyed hair, it no longer correlates with youth. And it certainly doesn't correlate with innocence; the honest brunette who does not dye her hair, perhaps because she is not scheming to get a man, appears more innocent. Therefore, blond hair dye falls out of fashion and then blondes are once again mostly natural blondes and so the correlation reoccurs — restarting the cycle.
All inversions belong in Hair of Gold. Compare Blondes Are Witches (showcasing the prevalence of giving magical women blonde hair)