It looked like a special effect, but the colours over Jonggol had a straightforward explanation.

A towering cloud over the city southeast of Jakarta lit up in pastel shades, creating a rare iridescent effect that reportedly stopped traffic as onlookers filmed the scene.

According to WABC meteorologist Lee Goldberg, as cited by Popular Science, the display was not a digital trick or a traditional rainbow. It was an uncommon cloud effect caused by sunlight interacting with tiny droplets or ice crystals.

Footage showed bands of vivid colour shimmering across part of a large cloud formation.

Goldberg said the colours are easiest to see when something partly obscures the sun, such as a mountain or a denser cloud. That partial blockage can reduce glare enough for the rainbow-like colours to become more visible from the ground.

The display stood out because iridescent clouds are relatively rare and often short-lived.

“These vibrant displays usually appear near the sun and can last for only a few moments — making them a truly magical sight for anyone lucky enough to catch them,” Goldberg said.

Ida Pramuwardani, acting director of public meteorology at the Indonesian climate agency BKMG, told Detik News the cloud seen in the video was a towering cumulus formation obscuring part of the rainbow.

In translated comments cited by Popular Science, Pramuwardani said if towering cumulus clouds cover only part of the rainbow, the shape can appear broken and resemble a “rainbow cloud.”

That explains why the colours appeared attached to the cloud rather than arcing across the sky.

Pramuwardani said the clouds are not by themselves a direct sign that a storm is coming in. They are more likely to indicate that convective clouds are developing and that rain could begin soon.

Commenters on Goldberg’s reposted footage were stunned by the sight.

“Is that another dimension?” one user wrote.

“This is something from Mother Nature that we don’t see often. Thank you so very much for sharing,” another said.