Colour wells on the Document Palette

Hi all. I have a 13 of pages of paragraph text. The text fill is black (RGB 0,0,0) throughout. No pen outline. No graphics. However, the Document Palette shows four wells - none, RGB 0,0,0, CMYK100 and RGB 0,0,0 (again). I usually only have the 'none' well showing. I have no idea what the others are referring to. How do I find out?