The Colors Window is broken up into 5 major areas:
Select whether you would like to pick your primary or secondary color.
Click this to view additional color selection options.
This shows the currently selected primary and secondary colors. There are also toggles to swap the primary and secondary colors and revert them to black and white.
Used for color selection.
Used to manage palettes. For greater discussion of this functionality, please visit the Working with Palettes section.
The Colors window has two modes of operation: "Less" and "More". By default, Paint.NET starts up with the Colors Window in Less mode. In this mode you may easily select a base color using either the color wheel or the palette. Paint.NET allows you to have two colors selected, a primary color and a secondary color, and you may use the drop-down box at the top of the Colors Window to choose which one the Colors Window is currently being displayed and configured.
You can also use the shortcut key 'C' to quickly switch between primary and secondary colors.
If you click the "More >>" button, the window will expand to present more detailed and fine-grained information. In this mode, you may specify the exact value of each of the color's components in either the RGB (Red, Green, Blue) or HSV (Hue, Saturation, Value) color space. Editing the color in hex, or hexadecimal, mode is also possible. The alpha, or transparency level, may also be configured.