Opportunity is missed by most people because it is dressed in overalls and looks like work. - Thomas Edison
Select the empty shape you want to color, then go to menu: Select>Same>Fill ColorThat should select all the empty filled shapes within and probably around the skull, then select a color to fill. This might be skipping a step if the shapes aren't "separated". Kind of heard to explain in type
Open Skull ImageMake a yellow box bigger than the skull imageplace the box behind the skullyou will now see yellow where there is no black in your skullselect both imagesopen your pathfinder windowClick on the divide option under Pathfinders:Ungroup your imageSelect the yellow out side your skull and delete as it is now extra/extaneousselect any yellow spotgo under select in your drop down menugo to "same" fly our menueselect "Fill Color"you have now selected all the yellow in your skullgroup all those together.Boom