SAUSALITO, CA – General Motors will hew to a fine line while styling the electrified vehicles it will bring to market in the coming years, looking to strike a balance between designs that accentuate the uniqueness of the cars and trucks but do not depart too far from a proven formula.

“Electric-vehicle owners want something different than their neighbors,” says John Cafaro, director-Chevrolet exterior design and lead designer on the ’13 Chevy Spark battery-electric vehicle.

“But it has to look appealing; it can’t look like a science experiment,” Cafaro says during a presentation linked to the Spark EV’s media preview here. “So you have to bring out those small electrification cues.”

As the first modern BEV from GM since the EV1 bowed in 1996, the Spark BEV adheres to the A-car segment’s familiar 2-box, 5-door design.

In fact, it differs very little from the internal-combustion-powered Spark launched earlier this year, except for a grille and an active lower-front air-dam design borrowed from the Chevy Volt extended-range electric vehicle.

The rear of the Spark EV takes on a subtly different look, owing mostly to the fact it does not have a tailpipe and the driver’s-side front panel adds a charging port.

The biggest difference is found on the interior, where the instrument panel looks more Volt-like, with high-definition displays of the BEV system. Electric Sparks also have a touchscreen on the center stack for displaying additional power information.

“We’ve done just enough” to differentiate the Spark’s aesthetic from its ICE peers, Cafaro says.

Ironically, Cafaro chooses a product from one of GM’s key competitors to underscore his point – the Toyota Prius. “Design played a big role in its success,” he says of the hybrid EV, contrasting it with the slow-selling Honda Insight. “Honda chose another direction with the Insight.”

The first-generation Prius, which bowed in the U.S. in 2000, sold 52,170 units over its 4-year run, according to WardsAuto data. An oversized greenhouse contributed to its odd proportions. Sales soared with the more contemporary-styled, second-generation model. Deliveries between 2003 and 2009 hit 665,411, WardsAuto data shows.

Combining the third-generation model and its new range of variants, the Prius to date has accounted for 1.3 million sales in its lifetime. The edgier Insight, meanwhile, has sold 76,276 units over the same timeframe.

Toyota stuck with it,” Cafaro says. “They have a good design and proportions, and they understand their customer. It is a good formula.”

Expect GM’s EV designs to evolve similarly. The Volt, for example, will become “more monochromatic and road-hugging” in its future iterations, Cafaro says. He describes designs for other alternative-propulsion vehicles in development at GM as “sleek, muscular and aggressive,” suggesting the auto maker wants to please many consumer tastes.

GM already is claiming the upcoming Cadillac ELR, which will use the Volt’s propulsion system, will sell more on styling than its electrified powertrain when it arrives in late 2013.

“We’re looking at all the different design DNAs as we go forward,” Cafaro says. “We have four brands. We can do a lot of things.” He also notes his team plans to closely watch the Ford C-Max Hybrid with its high roofline that creates tall proportions.

Cafaro stops short of offering what he considers the optimal design for an EV: “As long as vehicles are designed and engineered by people, you’re O.K. But there are timeless design elements that must be conveyed and never change,” he says, citing the Bauhaus and Frank Lloyd Wright schools of design and a product such as the P-51 Mustang fighter/bomber.

“Certain ingredients transcend time,” Cafaro says.