Comment by KineticLensman

>> So e.g. when the light is pure orange, it falls down into red wavelength range and is counted as red

'Pure' orange light isn't red. It has a wavelength of 590–620 nm. Red is 625–740 nm and Green is 495–570, so 'orange' is between red and green. The sensor filters each allow a range of wavelengths through. So green is triggered as well as the red filter. In RGB terms orange is 255, 127, 0, i.e. with a strong red component and a smaller green component.

White balance is computed downstream from the sensor, and is used to resolve the effect that a coloured light source creates a colour cast on objects, most noticeably on white ones. The human visual system auto-compensates for this but cameras require special processing, sometimes done using presets for different types of light (sunlight, shade, tungsten etc).