Inkist is your drawing tablet's best friend. It takes the features artists need: Layers, blend modes, customizable brushes, and more, and packages it in an interface designed to launch quickly, get out of your way, and let you work.
If you want to try before you buy, check out the lite version.
I wrote Inkist for one simple reason. I love my drawing tablet, but I've found that despite the fantastic power available in existing apps, they are cluttered and annoying to use. Inkist is the result of my work to fix that. For more on the initial development of Inkist, see my blog post on it.
Inkist's color palette gives you not only the ability to store the colors you're using, but also sliders to non-destructively change the brightness and temperature of the entire palette to adjust to different lighting conditions quickly and without cluttering up the palette with different shades of each color for each situation.
Clicking on the selected color will also bring up your Mac's built-in color picker, allowing you to use the standard interface for color selection.
Inkist shares its back-end with Filterstorm and has inherited a number of powerful tools. Aside from the image format and layering abilities, the curves and blurring tools come straight from Filterstorm. However, the HSL control shown here is something new, allowing you to easily change the colors of a layer.