Congrats and Welcome!! I've also had trouble picking colors. As of today I'm going with turquoise but not too sure about a secondary color... coral definately goes though. Here's a website that may help a little The Perfect Palette
I read a blurb from "Destination Weddings for Dummies" and some colors that they say are great for a tropical weddings are lemon, lime, tangerine, hot pink and turquoise.
Good Luck!!