Melt outsides in double boiler, being really careful not to let it burn at all (tastes worse and doesn't stick to insides). Once barely melted, remove from heat and drop in balls of inside, coat and remove. When the chocolate gets too hard, re-heat.
Make colored tops with just a tiny bit of color in water and sugar. The canonical chart for coloring is:
I use the microwave for melting chocolate: the double boiler isn't any better and is a lot more hassle.
When I want to make them vegan I use the solids from coconut cream.
I tend to eyeball things a lot.
For raspberry truffles, extract does not capture the flavor very well. Instead I'll use frozen raspberries. I'll melt ~equal parts coconut cream, frozen raspberries, and chocolate and mix well. If it's too watery you can add more chocolate. This needs to be well frozen to be covered, or the chocolate shell won't stick. If they start to warm up while you're dipping the chocolate in the dipping container will be lost. Keep most of them in the freezer while you work on small batches.
For hazelnut truffles, put toasted hazelnuts in the food processor. Use a collander to sort the powder and small chunks from the large ones. Mix the small in with the ganache, and reserve the large chunks for topping.