Ok, here is STEP 3 which deals with whitening. If your bones or skulls still have dark spots on them see STEP 2 again or read on.
If your bones or skulls still have dark spots in/on them this is grease. Sometimes a soak of whitening and then returning to STEP 2 will help loosen the grease so you can try step 2 again now or do a short version of step 3 to shock the grease and then return to step 2 (step 3 will need to be revisited).
Some people refer to whitening as "bleaching" but bleach has nothing to do with the process! What you need to use is Hydrogen Peroxide. A 24hour soak in the stuff should be enough to whiten your bones. Various people here have various rules on the time but you don't want to soak it longer than a few days.
HP can be reused so if the stuff is still foaming when I take the bones out, I re-bottle it. It does tend to have a short shelf life but if there's foam, it's still good!
Once out of the peroxide I rinse the bones off under the facet or dunk them for a short soak in clean water to leech the peroxide out. You don't have to do this, it's just a quirk of mine to get all the stuff out of the bone before calling it "finished".
Let them dry for a few months now before moving onto step 4. Sometimes I place them in front of a fan for a few weeks to help speed the drying. Remember, bones and skulls are very porous materials, it can take months and even years for moisture and grease inside them to surface if just left to sit. Heat and moving air can help speed the process.