It depends what it is you want to colour. For example, for coloured text,
open the Font dialog (from Format > Font, or via the Style Modify dialog),
and select "More colors ..." from the palette that appears from the Font
colour dropdown (you can also get to the palette from the dropdown menu
beside the Font Color button). "More colors ..." opens a "Colors" dialog -
choose the Custom tab and experiment with changing the RGB values directly
or by moving the colour sector cursors.
You can also use different colours for borders and shading, graphic objects
and so on. The "Colors" dialog is generally available from a "More colors
...." option in the same way.