Why does infrared appear purple in digital cameras?

Camera manufacturers typically do not spec the response curves of their sensors. Sensor manufacturers do, though. Here is the response curve for a modern sensor: Your digital image sensor has a surface covered with photodiodes (and other stuff)... read more

All of the sensor elements (red green and blue) are slightly sensitive to infrared light. In most cameras, the red sensor is most sensitive to infrared light, followed by the blue and then the green sensor. So if the camera is pointed at an infrared light, the sensor records something like 60% red, 30% blue, 10% green. This produces a purplish image. read more

On the other hand, since different cameras have different filters for their color pixels, what color you get also depends on what camera you use. When I took a picture of a remote with a cheap webcam I got red instead of your blue/purple. read more