I like to use a piece of phenolic to reinforce the tip. I typically like to try to color coordinate it with the bow.
On top of the phenolic, I'll use one of the woods used in construction of the bow. Sometimes I'll use bone, antler, or horn. Just depends on the bow.
For an accent in your riser, you might use whatever wood you're using as a core. Maple for example. IMHO, accenting with the core wood kinda ties the bow together visually.