You can pick any color, copy the #value to the clipboard and paste it into your message. You also can use the color name in your scripts. E.g.
<font color=#FF0000>your text</font>
is equal to
<font color="red">your text</font>
The color chart must be closed after viewing and using in order to continue your message.
IF you want to keep it open while working, explore to \MM_Data\MM_System and open the 'colorchart.htm' file.