When a child mixes fingerpaints to create a new color, is she using an additive or subtractive process?

Lina went in camping woods. while camping, she accidentally touched a strange planet. her hand immediately started itching, and her skin erupted in hives. after she gets home, her grandmother cooked some oatmeal, wrapped it in a cloth, and put it on lina affected hand. lina’s grandmother followed a traditional what remedy.