If you've opted for a tropical wedding day under bright sunshine, then you need to go for BRIGHT colours.
That's oranges, limes, lemon yellows, fuchsia pinks, turquoises .... go down the pastel route and the shades won't be able to hold their own in the bright light.
(Although white is actually alright of course.)
I've put together this moodboard in citrus shades with some bridesmaid styles in different necklines ... and you'll find plenty of other options at Dessy.
I'd also think about the temperature - if your maids are going to walk along a sandy beach then a short cocktail frock would work well - think chiffons and light fabrics that move.
And flowers? I'm thinking shades that contrast - talk to your wedding planner about what's available locally.
Dessy's Twist Wrap dress is also a classic for a tropical wedding - it packs beautifully, shakes out on arrival and comes in a multitude of colours. And it's the dress that suits every girl (because she can wrap it the way she wants) and will be taken out of the wardrobe again and again ...
One of Dessy's Twist Wrap dresses in Buttercup. What colour will you choose?