What do you understand the rules to be on using 'du' and 'Sie'?
Is it usual to use 'Sie' until something else is offered?
Confused in Germany
In addition to splattne's answer, it also depends on where you meet the husband.
If you're very close with your colleague and, let's say, she invites you to her birthday party, then it would seem a bit awkward if you say "Sie" to her husband. However, if you only know her from work and meet the husband on a business event, you should really start with "Sie". He will tell you otherwise, if he thinks you should use "du".
General rule: a "Sie" can easier be switched to a "du" than other way round. Better seem a bit too stiff than rude. ;-) You can always loosen the formality, but it's hard to take back an insult (which an unfitting "du" is considered as).
So, whenever in doubt, use "Sie" first and don't be offended if it is corrected. It's meant as a nice gesture.
Regarding your specific question: if the situation is not a very formal one, I would say it's not offensive calling him "du" from the beginning, especially if you're the same age or if he's not much older than you. I would hesitate if the couple was much older. Some people would see it as lack of respect.
The common rule is between total strangers of a certain age (depending on the situation, but's let's draw the line at 30) to start relating to each other in the "Sie" form until one of the two or the group offers to call each other "du".
On the Internet this rule doesn't always apply though. My personal experience is that I rarely use the "Sie" on discussion boards or services like Twitter.
I would base my actions on the relationship of the wife to the husband.
If I, the wife, and the husband were all about the same age, I'd use "du."
But if the wife and I were middle managers, and the husband were a CEO, senior professor, or prominent politician some 20 years older, I'd use "Sie," until invited to use "du."