First gen: Astral Black
Second gen: Velvet Black
But then I'm biased ;-). My first IS was black and it looked the dog's danglies when it was clean. My second was Platinum Ice and that looked great even when it had been driven through mud. Black ones worked with the smoked rear windows, but the silver-backed Lexarse lights (as they call them on http://www.barryboys.co.uk) looked a bit naff. In silver, this problem went away, but the smoked windows looked a little out of place IMHO.
I wasn't allowed to have a second gen IS in anything other than black. I did suggest silver, but SWMBO told me otherwise.... It pains me to say it, but she's right.
[EDIT]
SWMBO has just looked over my shoulder at this post. The conversation went something like this:
"You only have to drive down one road to decide what colour Lexus to have, and that's the A47 into Leicester. If you see a new gen IS coming towards you and it's silver, you think "mmm nice car". If you see a new gen IS coming towards you and it's black, you think 'f**k me, what's that? Phwoaar!'. "