My understanding is that "Double Optic" Headlights have nothing to do with the gas type. Single optic headlights have one reflector and one bulb with two filaments, one for high beam, the other for dipped beam. "Double optic" headlights have one reflector and one bulb for main beam, and one reflector and one bulb for high beam. So it looks like four headlights. The new MX5 has double optic headlights for example, but they are not Xenon gas.
Mini lights are double optic as standard arnt' they ? Upper area for dipped beam, lower seperate area for high beam.
If i'm wrong, may the hand of god strike me down.
PS. Have a look here. No mention of the Bulbs being specifically Xenon Gas for the conversion!
Blue and bright isn't really the test anymore, many companies produce high-intensity halogens with a blue-tint glass.
Have someone else turn on the lights while you're looking at them. If they hesitate slightly, sort of a on-ON step-up to turning on, they're HID lamps. All the HID lamps so far seem to come from just a few manufacturers, and do this little gas ballast start-up sequence.
If that isn't obvious (too fast, like on a Porsche) then try to look at the bulbs. If there's a filiment, it's halogen. Nothing? Then it's HID.
The headlamp fuse can also be a giveaway. HID lamps 'usually' require a lesser fuse than halogens.
Although, that might be a little obsessive to check. You'll know eventually... the super bright halogens burn out pretty quickly, where the HID lamps have an operating life beyond the car.