I'm not sure what PIAA is using these days, but I still have a set of PIAA Projector Ion Crystal fogs. On my ARB just for looks, not wired up. The blue coating is actually blue because of it's thickness. At even fractions of wavelength thickness, a layer will reflect that frequency light while passing other frequencies. Sort of a band-pass filter. It has to do with internal reflection within the layer. I tried to avoid that when making optical coatings for LCD glass, they used it to advantage for foglights. Their theory is that the internally reflected light adds heat to the filament, which gives off more broad-spectrum light. That should be more efficient. The same bulb could filter out blue, giving amber for foglights, or filter out longer wavelengths, giving blue. They only have to change the thickness of the coating deposited on the glass, at no cost to them. It's a simple process, not much to mess up. Sunglassed are made that way fairly cheaply. I can't imagine they've switched to painting the bulbs with some kind of blue tint, that might be more expensive to get right. I'm a fan of Hella, not into funky blue light, and prefer white fogs, so I haven't used PIAAs in many years. I'd like to try their half-coated hi-low bulbs in my inboard lights, just for looks. Got other priorities first though.
