I expect this is NOT due to the white balance of the camera adjusting to the ambient light. After all, your eyes adjust to the ambient color too. More likely it is due to two factors:

1. The spark is a broad-spectrum emitter. It emits significant light we can't see. While the camera sensor is balanced to result in close to the same color we perceive for visible light, it will react to invisible light unpredictably. This is why there are UV and IR filters over sensors. These invisible wavelengths will register on some sensors, but result in strange color. What's the right color to display for something we can't see?

   The spark is very bright compared to its surroundings, so some of its energy in the invisible part of the spectrum will make it thru the filters and register on the sensor as unpredictable colors anyway.

2. The spark is very bright, compared to the rest of the scene that the camera has set its exposure to. As a result, the middle of the spark will almost certainly be overexposed. This means that the R, G, and B values will be clipped to 1. As soon as a color channel gets clipped, the color balance is lost. If the red and green channels are more sensitive, which is often the case, then a neutral gray will have a lower blue value that the others. When all the channels have the same value, as when they are all clipped at 1, then it looks like the blue component is brighter than the others.