Exactly, wear whatever it is that you want :)
I wouldn't be too matchy, but instead, pick complimentary colors. Say, he wears a white button down with a pair of khakis... Well, with that, you can wear pink, aqua, purple, yellow, etc. :)
I don't know what you are comfortable in, but I love wearing sun dresses for things like this. :) Otherwise, wear jeans and pair them with a nice blouse that's not too busy.
Or, if you are both huge sports fanatics (for example), wear your favorite sports jersey. My future brother in law and sister in law had rivalry football teams. So, for some of their shots, they wore their jerseys :)
Hope this helps you out a little!! :)