Now that more than one million hybrids have been sold, one might think that automakers have figured out how to sell environmentally friendly vehicles. With demand for “eco” cars at an all-time high, the approach to this growing market segment is more critical than ever. However, based on current marketing moves and machinations, no single technique has emerged as the winning tactic.

Different auto companies are taking distinct approaches, ranging from almost invisible badging on models that are virtually identical to less environmentally cars—to unique hybrid-specific models like the Toyota Prius. The confusion is exemplified by recent steps taken by European automakers Renault and Peugeot, which are setting up “mini-brands” that feature only the companies’ top environmental vehicles.

Renault launched its “eco2” brand and fellow French carmaker Peugeot is rolling out its “Blue Lion,” not to be confused with the “Bluetec” and “Bluemotion” labels used in association with clean diesel technology for Mercedes and Volkswagen respectively. (Apparently, blue is the new green, which is the new black.)

What do these labels really mean? Peugeot and Renault have fairly strict criteria for models to qualify for the environmental badging—greenhouse gas emissions of less than 140 g/km, 95 percent recyclability, and low-CO2 manufacturing.

For example, the Renault Logan eco2 achieves an incredibly low 97 g/km of CO2 and was a featured entry in last year’s Challenge Bibendum. Eco2 and Blue Lion focus on manufacturing processes as well as fuel efficiency. Renault said that it plans to expand the eco2 branding throughout models in the Renault-Nissan automotive world. Meanwhile, VW’s Bluemotion diesels and European an entire line of vehicles called “Prius.” That idea apparently is going nowhere.

The General Motors eco-sub-brand for hybrids called “Green Line” has also made little traction. Perhaps that is, in part, why GM’s Volt, a plug-in hybrid due out in late 2010, will be released as a plain old Chevy.