Green is the new yellow for Wellington buses, with the first batch of new buses for Wellington's streets arriving from the UK.
The new buses are diesel powered, but manufacturers Optare say they are almost cleaner than fresh air.
The buses were custom built to suit the needs of Tranzit, which looks after 60 percent of the region's bus routes.
The regional council had opted to paint them a lime green, with a yellow front - moving away from the iconic black and yellow of the city's buses.
The Euro 6 compliant engines are what make the emissions on the diesel-powered coaches so low, Optare president Graham Belgum said.
"This is almost putting out air that's cleaner than the air it draws in. That's how good Euro 6 engines are."
In the back of the bus was a large chemistry set that purified the air coming out of the engine.
Tranzit's 235-strong fleet will have 114 Optare buses and also include 10 electric double-deckers, built by Tauranga company Kiwi Bus Builders.
The company was putting its reputation on the line by moving into the capital, Tranzit's managing director Paul Snelgrove said.
"Wellingtonians are very passionate about public transport, we've got a lot to live up to."
The Greater Wellington Regional Council caused controversy when it made the decision in 2016 to get rid of electric trolley buses - to replace them with a combination of diesel and hybrid vehicles, with a plan to move to an electric fleet.
Tranzit has 10 electric double deckers heading to Wellington and Mr Snelgrove said the company was committed to bringing in as many electric buses as it could.
The company had come under fire over its new driver contracts, with the the union, Tramways, taking them to the Employment Relations Authority (ERA) over pay and conditions.
Tramways wanted Tranzit to roll over the contracts bus drivers moving from incumbent NZ Bus to Tranzit, but the new operator would not.
The case was expected to be heard by the ERA later this month.
Greater Wellington Regional Council chair Chris Laidlaw said he was confident the new company would treat its staff well.
The reason Tranzit's bid to run buses in Wellington had been so attractive to the council was because it was the only company committed to moving to an electric fleet, Mr Laidlaw said.