Press the color swatch squares in property panels to launch the Color Picker and select a new color.
To pick a new color click on the color spectrum. Each new color you pick changes the bulb color on the canvas and in the render view to provide instant visual feedback as you make your color decisions. Having picked a color on the spectrum use the color tuning grid for fine selection. The magnification buttons select a range of similar colors centered on the selected color. Magnification x16 gives a wider range of colors. Magnification x2 gives a narrow choice. Use the value control to change the brightness of the color - although brightness is typically controlled using the Brightness slider for the bulb.
You can lock the hue and just vary the saturation by pressing the Ctrl key and moving the mouse vertically on the color spectrum. To keep the same saturation and vary the color, press the shift key and move the mouse left and right.
Ctrl - Hue Lock
Shift - Saturation Lock
To save a favorite color just drag a color from the tuning area to the user storage area. Colors stored here are saved in your project file.