Re: seriousness, that's kind of the point. I can appreciate one liking other colors but the idea is that a wedding is one of the most important days in one's life and the occasion generally demands a certain amount of formality / seriousness if you will. If you are truly dead set against these colors, consider a light grey. It still is best during the summer IMO but is less obviously a summer color. I'd suggest it more as a lesser evil than a true recommendation, but there you go. The other thing to consider is that if you usually would wear a suit in the evening, darker colors are simply more appropriate and look much better. Lighter colors work best during the day and during summer.