Practically speaking, I would get a navy suit in an all season weight, and not a summer weight. Your navy suit is your go-to for job interviews, presentations, etc., generally speaking. This would end up requiring you to own two navy suits, one of which you'll rarely wear. You'll rarely go to your closet for a summer event, looking for a suit, and say "I think navy is the order of the day." A summer weight suit is best in a light colour, as you'll get the most wear out of it that way. I'd stick to your original plan, both to coordinate better with the rest of the wedding party, and to get the most out of your investment in the suit in the long run.
Actually this idea came from comments on another thread where it was pointed out that 'you can't have too many navy suits'. I was originally opposed to the idea of wearing navy solely because I am a 1st year lawyer with only 2 suits to my name one of which is already navy and I need to expand my wardrobe but all my savings atm are going to the wedding. (I work in the suburbs so its ok to wear more casual suits on days I'm not in court). Re: Summer weight. Given I'm in Australia and the wedding is outdoors in February there is a very real chance we will be looking a weather around the 40C mark. I could still go a different colour than navy but my groomsmen will not own any suits in less formal colours. I think If I wore a beige or brown or some such and the rest of the wedding party ended up in navy/charcoal I may look a bit underdressed for my own wedding.