Lucie is the "golden-haired doll" who charms just about everyone she meets with her beauty. She’s got yellow hair, as you’ve probably guessed. More interestingly, however, Dickens uses her hair color as an image that binds her family together. She becomes the "golden thread" that unites her father with his present, not allowing him to dwell too much in the horrors of the past.
A golden thread almost sounds like some sort of magical power; in fact, the Manettes lead a "charmed" life in Soho. Lucie may not be the character that gets the most screen time in this novel, but Dickens makes sure that we all know she’s its heart. Lucie unites Carton to Darnay, Dr. Manette to Darnay, and Mr. Lorry to the family in general. Lucie becomes the reason that Charles escapes the grasp of the Republic’s "justice."
In one terrifying moment of the novel, Jacques Three speculates about how wonderful it would be to see her golden hair on the chopping block of La Guillotine. The charm of Lucie’s influence, however, makes this an impossibility. Mr. Lorry and Sydney are determined to save her at any cost. Guess being a blonde has some good points, after all.