Yeah, I don't think tropical or monotone would be good.
But, you could use any earth tones [green - blue - rusty - tan - grey - ochre]
especially if they are more unusual - then have a few images carry out the rest of your themes: adventure - relaxation - culture - the sea, etc.
There are a gaggle [flock, bunch?] of web-based tools for choosing colors, too
as I'm sure others will link here for you: just make the first tone you begin with
is the one that really matters! [Or, search for "color picker/schemer/chooser"...]