Notwithstanding the long debates on here about the legal issues relating to HID kits, I'm a big fan of these kits and have had them fitted to all my cars for years now.
Therefore I thought I'd post a brief account of my experience in terms of bulb colours as I know this is often a common query from prospective buyers.
The most common colour bulb specified and indeed sold is 6000k which typically gives you a blue tint synomonous with Standard fit Xenons. However the actually colour depends on a couple of factors firstly the wattage of the ballasts / bulbs being either 35W or 55W the latter offering considerably more light output and without the bulb error messages. The 6000k 55W kits offer a brighter more OEM Xenon colouring than the 6000k 35W kits that are typically very blue and clearly stand out as aftermarket fitment.
The second factor is dependant on if you have a projector headlight unit or reflector, the projector units as fitted to the 159 greatly help to correct the light pattern that is slightly off as a result of using the incorrect bulb for the headlight design. However to clarify I've never encounted any issues with beam patterns on projector lenses. The projector lenses also help to give a slight blue tint to the light colour particularly at the edges of refraction.
Accordingly I've tried various colour combo's and have now just tried the new generation of 5000k 55W kits, which is now my prefered set up. The colour is very pure white with the slightest of blue hints, and is the closest to OEM colouring I've found to date. The 6000k kits are good and obviously Xenons but also clearly stand out as being aftermarket and to the trained eye, I for one can spot these kits a mile off.
However this latest 5000k 55W set up is spot on IMO and very close to OEM, the light output is immense albeit I have been running on standard Halogen bulbs for two weeks so the difference is probably exagerated. For those wondering the difference between standard halogen bulbs and 55w HID Kits is as clear as night and day. For a start I can actually see where I'm going in the dark now compared to the standard candle like set up.
For reference the 4300k colours are too yellow and just appear to be bright halogen bulbs so do not give the illusion of standard Xenon headlights. The 8000k bulbs and higher k colours are just for show and do not give the level of light as the lower colours plus the colour rendering is awful especially with the pinky / purple colours, I personally would avoid this.
So to summarise if you want a standard Xenon appearance in your 159 / Brera I'd suggest the 5000k 55W HID Kit's, The kit I've just purchased cost £38 inc P&P and is as good qaulity wise as the £200+ kits from suppliers such as HIDS4U (yes I've bought kits from here to enable me to jusitfy this statement).
I've not bothered with taking pictures as you can't really tell from pictures as to the actual colouring and the bright light distorts the camera image. Also to claify the above statement is based solely on my own personal experience of buying and fitting 30+ different kits on friends, family and my cars over the years.
This is kit I've just fitted in case anyone is interested...