Basically that is true. HID’s do not change intensity. The bulbs come 3 ways
1)Fixed position bulb (of a given color) 2)Bi-Xenon (low and high beam, there is a small magnetic motor that retracts the bulb for high beam, it doesn’t get any brighter just higher) 3)There are some with a halogen bulb attached to the HID for high beam. Doesn’t really do much except get you through inspection if your state checks high beams.
Lastly would be projector HID’s. In these the cutoff shield moves down when the high beams are turned on. Again not any brighter just higher (and farther).
The brightness of the HID’s is controlled by the ballast, either 35 watt or 55 watt. The color is controlled by the bulb.