Darken or Lighten brush/pencil?

Is there a darken or lighten brush/pencil so that I can just draw over areas willy nilly to incrementally darken or lighten them. I have to be missing an obvious tool for this. Or do I have to make more colors on palate and adjust each shade individually/use gradients?

There is nothing like that available in Harmony. You could use Line Building Mode and a brush with a degree of transparency to achieve a darken effect. For lighten you could use a transparent eraser or transparent brush/pencil that is the general color of a background with potential success depending on the circumstances.

Thanks! Definitely gets me in the right direction