Brown isn't bad.
Here's a link on what a good spark plug looks like. Which one do you think yours is?
If you do a lot of city driving, then then can foul up a bit. Give your car a quick flogging and check the plugs again!
Are there black carbon deposits or oilt build ups?
Are all the spark plugs the same condition. Usually if one is different than the others, it could point to a problem with that cylinder. (plug/injector/lead etc).