Sarah Pidgeon earned every strand of that blond.

The “Love Story” actress, 29, shared in a new Vogue Beauty Secrets video that it took more than 20 hours over two days to transform her naturally dark brown hair into Carolyn Bessette Kennedy’s signature shade.

“I went in to audition for Carolyn with long, dark brown hair, and have since gone blond, which is a whole process,” Pidgeon said, adding that she and her team “have to be really careful because I have psoriasis, and obviously it’s quite an intense treatment, sort of lightening such dark hair.”

The actress uses a steroid on her scalp to manage flare-ups, which can be aggravated by the dyeing process — and by her diet. (“I have yet to have the self-control to get rid of gluten, or dairy, or sweets,” she admitted.)

But the lengthy transformation served a purpose beyond just matching Bessette Kennedy’s look. Pidgeon said the hours in the chair helped her step into character, calling the process “so pivotal in helping me just spend time sitting in the chair watching this transformation happen and leave behind a bit of Sarah.”

Her hair also evolves throughout the FX series, mirroring Bessette Kennedy’s own style arc. “In the beginning, it’s much more curly, and there’s more dimensionality, just maybe some more low lights,” Pidgeon explained. “And then throughout the show, it gets much blonder, much straighter.”

Bessette Kennedy’s real-life colorist, Brad Johns, previously spoke to Page Six Style about the late style icon’s hair, describing it as “darker at the bottom” with “brilliant gold pieces” up front.

Johns, who famously took Bessette Kennedy from light brown to a buttery blond using his signature “chunking” technique, initially had concerns about early production shots, telling us it was “just wrong.”

That buttery shade was so central to Bessette Kennedy’s identity that when she asked Johns to dye it black in a panic before her 1996 wedding to JFK Jr., he refused — and brightened it instead.

Pidgeon, for her part, plans to keep the blond for now — and after all that, who could blame her?