White gouache can be a fantastic tool for adding final highlights to sketches. It can make cat whiskers, snow, or sailboats pop right off the page, especially on toned paper.
Create bright whites and pastel tones
Since watercolor and gouache are both water-based paints, you can mix them to create more opaque pastels. Try adding them to earth-tones for a range of sandstone and beach hues.
Another tool you might like is the Gelly Roll Pen. It’s perfect for creating really fine details, like the ribs on a very small feather.