Mike Bersell, CEC
I have used the freeze dried powders for chocolate work. They do work great for flavour in ganaches, but are very expensive. I've also used them to colour white chocolate, and they do work, as they contain no water, but again, the sources I've had make it very exensive. I'm now fooling around with colouring white chocoalte with spices and flower petals.
Here is another easy way to make fruit powders. Simply use a veg peeler to remove the outside skin from your citrus of choice. Try to get as little pith as possible because all you really want is the outside skin. Thats where all the fragrant, flavorful oils seem to hang out. Place the skins in that dehydrator that you have laying around and never use. Dry them out let them cool and them grind in a coffee bean or spice grinder. I like to plan ahead and use the powders fairly soon after grinding. Like any spices, the longer they hang around, the less potent they are. I never used to use my dehydrator but now it's on constantly. I also dehydrate hot and sweet peppers, mushrooms, meringues, fruit papers and more.