A Darwin business recently did something very few might have done before — it turned the air-conditioning temperature up in November.

Cooler temperatures and mystery were in the air after RSL patrons repeatedly observed how much colder the building had become.

Staff stopped lowering blinds over windows that were previously too hot to touch, while balcony regulars noticed the cold change.

"The one I like most is the fact that our members inside the air-conditioning are saying that the air-conditioning is now too cold," president Don Milford told ABC Radio Darwin's Conor Byrne.

The cool change coincided with a large white wall adjacent to the building being painted over with bright colours.

But the RSL committee weren't drawing any conclusions.

"We haven't had time to confirm anything through electricity bills, however we have had repeat comments from patrons," treasurer Kerry Mader said.

"But at the moment it's all subjective."

The sudden drop in temperatures left RSL Darwin president Don Milford stumped. ( ABC Radio Darwin: Jesse Thompson )

Elsewhere in Darwin, another business opposite a newly painted mural also reported a reduction in heat.

So could colourful street art be inadvertently saving these businesses on their electricity bills?

Walls in black won't send heat back

The answer is yes, and the reason is tied to the fact that the roof on your house is probably a light colour.

According to architect Lawrence Nield, white walls and surfaces reflected almost 100 per cent of sun radiation, so the unpainted wall was a source of heat.

"With the mural on the wall, it's cut down the reflectivity, so the heat is not being reflected across to the building in the same quantity as it was before," he said.

Professor Nield, who works on heat reduction strategies with the Northern Territory Government, said the body's sensitivity to even minute temperature changes would have prompted patrons to comment.

But he also said the RSL's asphalt car park posed a more significant problem because asphalt absorbs and stores about 98 per cent of heat.

This means that even when Darwin's ambient temperature is in the low 30s, the city's streets could be reaching the high 60s.

"When the asphalt heats up to 66 degrees, it then re-radiates or emits the heat," Professor Nield said.

"What makes Darwin feel so hot and makes it unpleasant to walk, say, from Cavenagh Street to Mitchell Street, is that radiating temperature of the bitumen and also from some of the buildings."

A tree is worth an air conditioner

Architects and urban planners have long begun to take these principles into account.

In fact, California has adopted white roofs into its building codes.

Professor Nield also said a tree with a canopy five or six metres wide could be as effective as one air-conditioning unit.

"Trees and vines on frames are the best way to reduce heat on your house and in the city," he said.

"The colour of the building is also important, but the problem is if we paint everything white is that it reflects heat, perhaps into other people's backyards or into other people's buildings.

"So trees are the first and best way to do this."