The color picker allows you to select a wide variety of colours (millions in fact). You can create a custom color by clicking on the "Define custom colors" box. Just set your color using the tools on the right, then click on the "add to custom colors" box, then make sure you select the new custom color before you click on OK.
If you are using this dialog from the "Macro=>Color picker" option, when you click on OK it will copy your selected color number to the clipboard and can then be pasted in where required.
