The current color selected in the Color palette is displayed on a large corner square. Left-clicking on the square opens the standard dialog Select Color. Right-clicking on the same box opens a menu of available color modes: Grayscale, RGB, CMYK, and Lab.
By moving sliders or entering numerical values into the fields, one can change the individual color values of the selected color. At the bottom of the palette is a small spectral bar - bringing the cursor over this will cause it to take the form of an eyedropper. To choose a color just click the eyedropper on the bar.
The empty squares at the top right area of the palette are used to store frequently used (custom) colors. To add a color to the mini-palette just drag it from the current color box to a square of custom colors or double-click the left mouse button on a square and select a color from the Select Color dialog. To change the main color to that in a box, left-click on a box. To remove the color from a box, right-click on it.