Tomorrow's cars will scrimp on fuel, envelop us in safety, guide us to our destinations, impress us with intuitive features and comfort us with ergonomics we can't believe we ever lived without.

But for all that, these evolutions will never shield us from one of the most important questions a driver faces when choosing a car: Which colour?

And more specifically, if current trends hold: Which shade of silver?

In two separate surveys by major auto paint suppliers, silver remains the most popular colour for new cars of all kinds in North America, capturing 24 per cent of the overall market in 2006 by PPG Industries' numbers; 19 per cent in that year according to DuPont.

It's the seventh year running for silver, an unusually long term for a top hue.

But even the stateliest shade of grey is going through a transformation that's indicative of future trendy car colours: shifting, iridescent hues, which subtly change as you walk around the car or see it in different light.

Put another way, that new Mercedes, resplendent as usual in tried-and-true silver, may flash a hint of radiant blue or subtle green as it whizzes by.

``You're going to see a colour, and you're going to do a double-take,'' says Karen Surcina, colour marketing technology manager for DuPont.

It's what's known as ``elaborate neutrals'' - blacks, whites and silvers that are flecked with ``effect'' pigments to produce iridescence.

Iridescent colours are a product of light diffraction, not pigment. This means that minute surfaces - flecks of aluminum, mica or synthetic materials - embedded in the paint split light into its component parts, giving the illusion of depth or reflecting different colours. Depending on the angle, the eye might see blue, green, silver or otherwise.

The effect, in a word, is mesmerizing.

``Essentially it's because the human eye is fascinated by any colour that seems to have an undulating movement, something that appears to change,'' says colour consultant Leatrice Eisman, speaker and author of several books on colour, including ``Color: Messages & Meanings'' (Hand Books Press, 2006).

``There are some social anthropologists who have said one of the reasons humans are so fascinated by this is that it reminds us of water, which we can't live without,'' Eisman says. ``It seems like quite a stretch, but we see it in other areas too: a seashell, an oil slick in the street - it can be the most mundane thing, and yet if the colour seems to move, our eyes go right for it.''

As DuPont and PPS prepare data from the 2007 model year to present to carmakers this fall, the prevailing wisdom is that silver will hang on to the top spot for a little while, anyway.

Eisman says silver's popularity is due largely to our obsession with technology and gadgets. It is a reflection, she says, of the dawning of the digital age.

``Silver was once in most people's minds associated with the word 'classic,' but people are now responding by saying it's 'high-tech,''' Eisman says.

That said, there's no market force more powerful than consumers' perceptions of something as oversaturated or past its time. Eisman uses the example of the mid-'90s, when the introduction of teal cars put that odd colour front-and-centre, not only in parking lots, but in fashion and design as well.

``That blue-green was really like, pow,'' she says. ``We hadn't seen it since the early '80s, but it had taken a rest, and became the car du jour. But then what happens is, it gets so identifiable with a certain time period that people say, 'Oh, I don't want that.' Obviously, red sports cars are going to be here forever, but it's possible that silver will soon start to look a little tired.''

Indeed, both Surcina and Jane Harrington, PPG's manager of colour styling for its automotive coatings, say new colours are coming into vogue.

``Blues and browns, especially,'' Harrington says. ``Brown's a colour family that hasn't really been in the marketplace since the 1970s, and it looks really fresh right now.''

Some colours sell well in certain types of vehicles, but not others: Blue is already a colour of importance, depending on the car. ``For vans, it's something like 21 per cent of the market share,'' Harrington says. ``And on SUV's, it's more like nine per cent.''

In both surveys, the second most popular colour was generally white, which remains the default for the chronically nondescript, Eisman says.

``It's the same reason people paint their walls white,'' Eisman says. ``It goes with everything. Most consumers see it as not really making a statement.''

Eisman figures that about 10 per cent of the population ``want heads to turn. ... But that's not the majority of the population.''

Even if the majority doesn't want a sparkling, luminescent red, today's consumer definitely wants the option: Harrington said a survey at last year's auto show in Detroit showed that 68 per cent of potential car buyers would be more likely to choose one vehicle over another if the manufacturer offered a greater range of colour choices. Similarly, Surcina says DuPont's market surveys have shown that roughly 40 per cent of consumers will change their car choice if they can't get the colour they want.

With so much at stake, it behooves carmakers to put as much thought into colour options as they do styling and drivetrain features. So what's on the long-term horizon? Both Surcina and Harrington say we can expect an eye-popping level of vibrancy in the next decade or so.

``We're going to see a lot of colour coming back in,'' Surcina says, ``and it will be more bold and bright, with this hue shift. You can already see a lot of it on the road now.''