I will be building a cedar deck. I was planning to do the railings/posts in composite. The first reason for this was to give the deck some contrast and the 2nd reason is to avoid having to stain the railings and spindles. Now I am thinking of having the edge of the decking to be in composite to match the railings post. In essence the deck boards that will outline the frame would be composite, like a picture frame and then the balance of the deck would be all cedar.
I like your idea of contrasting woods to separate a have a more custom look. I think you will be fine with the composite I would recommend you apply a simple wood sealer made for decks just to help prolong the wood finish from weather and use. You can pick up a gallon at any Home Depot or Lowes type of stores.