SAN DIEGO – Teenage private eye Veronica Mars has gone from punky to preppy.

The title character of the CW series, with her quick, bright wit and sharp eye for life’s darker moments, has left high school and is going to college, doffing her dark threads and spiked tresses for something a little more stylish.

Just don’t call it “mainstream,” said Kristen Bell, who plays Veronica.

“It’s simply that she doesn’t feel the need to spike her hair up and wear so much black leather and stuff that’s tough,” Bell said of her character. “A lot of kids dress to conceal themselves a little bit … Veronica dressed really tough because she felt hurt and vulnerable and dressed to try to combat that. But now I think she’s sort of accepting who she is; she’s not feeling the need to be so punky.”

Bell, 26, but easily able to pass for 19, is wearing a neat beige suit, with her now-long, blond hair smoothed into a sleek ponytail, as she chats between scenes at a soundstage on the outskirts of San Diego, where “Veronica Mars” is shot.

This season’s changes are a natural expression of Mars’ new life and attitude.

How she is feeling is very much the heart of the show, and despite the new outer gloss, her emotions still run strong and deep.

“She was wise beyond her years, or jaded, however you want to call it. But actually being a young kid and wise beyond your years is slightly different from being an adult and simply being wise,” Bell said in explaining the subtle transition she’s aiming for with Mars’ emerging maturity.

Although she hadn’t seen upcoming scripts, Bell said, “I would hope that Veronica would choose to be vulnerable a little bit more. She’s so sarcastic, but she’s always funny and so witty, which is always great, but I think it would be nice to see her a bit more raw this year.”

Show creator Rob Thomas assured that however Mars looked she wasn’t going to lose her edge.

“My fear with the character is never let her get too huggable, too cuddly, too warm,” he said, noting he tells the show’s writers to “write her like a porcupine.”

In its third season, “Veronica Mars,” which usually gets better reviews than ratings, now airs Tuesdays at 9 p.m. on Channel 11, KSTW. The CW is the amalgamation of the defunct WB and UPN. “Veronica” aired on UPN it first two seasons.

Bell admits to a moment of trepidation that her series wouldn’t make the new network’s cut, especially when she heard that the CW had picked up “7th Heaven” and thought that family drama might fill “Veronica’s” potential time slot.

But, Bell said, “I’ve always had confidence in the show, and it wasn’t cockiness, it was just belief.” That faith could be tested, though. Only 13 episodes have been ordered so far, not the customary season-long 22.

Joining Mars this year at the local Hearst College are most of the friends with whom she shared high school adventures in the fictional Southern California beach town of Neptune. They include her best pal, Wallace Fennel (Percy Daggs III), and her boyfriend, Logan Echolls (Jason Dohring). She also, of course, still has plenty of time to stop by the office of her private investigator dad, Keith (Enrico Colantoni).