DCEB sent in this question. Designed to throw you - these questions work to either get your defences up - which is not a good thing as you might come across defensive or the opposite - get your defences down in which case you drop your guard and run the risk of blabbering.
With this question there's not an awful lot you can do with this answer. Yes there are heaps of books on the psychology of colours, black is dark, yellow is angry, red is dominant etc. It's best to keep your options open with "Oh that's an interesting question - I've lots of colours I love - green, red, orange, why do you ask?"
It's unlikely the interviewer has a hidden agenda, unless of course they've just completed a short course on the psychology of colours and now they're armed with the latest psychobabble. Which is why even if black is your favourite colour it's probably best to stay pretty neutral, just in case...