"Highlights lighten the natural pigment, and lowlights add darker pigment," Schaudt said. "Your colourist should pick whether you need either or both. You might even need midlights — which are lighter than your natural but darker than your overall — and a combination of all will give a high-end custom look to your colour."
That's the beauty in seeing a professional: you don't have to worry too much about picking which colour treatment is best for your hair, as your hairstylist should be able to identify what you need.