The Rainbow effect will occur when the light on the bag is stronger than the background light. Here are some examples:
Note: If you wear it in sunlight, it keeps dark gray and almost no difference in color, because the sunlight is too strong.
Here we explain how it works in detail:
When there is no natural daylight, sunlight or light from lamps reflecting off the surface, the bag is black and shows very slight to no color variations.
In natural daylight the first noble color changes are visible. Depending on the light intensity, these are stronger or weaker. In the sunlight the colors seem more saturated and intense.
Now it gets magical!
When direct light is reflected, the bag lights up in intense, bright colors.
The effect occurs in direct sunlight or through the use of your smartphone flash. Depending on the intensity and color spectrum of the light, the bag shines in different colors.
Here is a video how on it looks in the dark with a flashlight / car headlights