First, the solution: click on the oblong button in the top right corner of the Colour Viewer (Palette), it opens and closes the different view options, including the CMYK sliders. The same button is in most windows of your Mac, if you run OSX 10.4 version, and it is in iWork ’09 version windows.
What’s the CMYK option for? CMYK sliders give you precise control of colours in your document. If you prepare it for commercial (professional) printing, you can, for example, set the colour of black text to ‘true black’ by setting Cyan, Magenta and Yellow to zero and black to 100 percent. By default ‘black’ in Pages is a composite colour (see picture below) which is a mix of different CMYK colours. It looks good on screen, but in print gets fuzzy. Changing the setting to 100 percent black give text crispness. Even if you are not going to print your project commercially, when you make PDFs from Pages I suggest changing text to ‘true black’.
When working in a team, swap CMYK readings of graphic elements in your project to achieve consistent colour sequence.
The Crayons box at top right gives a selection of preset colours with fancy names, like Licorice for black. Click on the colour wheel at top left, drag the little dot around to create a new colour. Click in the rectangular colour window and drag the colour down to the color palette at the bottom of the window to store it if you intend to use it again. If you see a colour or a colour sequence that you like, for instance in one of the templates, store them in the palette and use in your project.
If for some reason the palette disappears, click on the little round ‘handle’ at the bottom and drag it down – the palette will open.
To open Colour Viewer you can use a keyboard shortcut: Command+Shift+C.