Colour is very subjective isn't it.
I guess you could just say 'I like it so I'm going to have it'.
Problem is thats fine if things like depreciation don't matter.
In all honesty MOST people wouldn't consider an IS in yellow - I'm currently looking so in quite a good position to judge. We (potential buyers) are trying to buy into a quality brand with a bit of a sporty edge, luxurious but not flash - to me thats the IS.
Now don't wish to offend anyone 'cus obvioulsy people out there will have these colours but IMHO:
plat ice nice but lots about - choice of the company car driver
blue - always looks clean, easy to sell on
red - for the brave, only looks good when spotless and gleaming - best colour for de badge
white - fine for the police but not for me thanks
green - classy, great with Oakham - understated
black - ah black, the colour for the IS - shows off the alloys well, suits the flared arches - all in all the best
Of course when all is said and done - if you like it then it's good !