These functions assist in calling particular parts of a theme's palette.
For example, ag_base() will return the current theme's base or background
color, and ag_highlight() will return the color used in that theme to
highlight one or more nodes, lines, or such.
ag_base()ag_highlight()
ag_positive()
ag_negative()
ag_qualitative(number)
ag_sequential(number)
ag_divergent(number)
One or more hexcodes as strings.
Integer of how many category colours to return.