This in primarily an internal openair function to make it
easy for users to select particular colour schemes, or
define their own range of colours of a user-defined length.Each of the pre-defined schemes have merits and their use
will depend on a particular situation. For showing
incrementing concentrations e.g. high concentrations
emphasised, then "default", "heat", "jet" and "increment"
are very useful. See also the description of
RColorBrewer schemes for the option scheme.
To colour-code categorical-type problems e.g. colours for
different pollutants, "hue" and "brewer1" are useful.
When publishing in black and white, "greyscale" is often
convenient. With most openair functions, as well as
generating a greyscale colour gradient, it also resets
strip background and other coloured text and lines to
greyscale values.
Failing that, the user can define their own schemes based
on R colour names. To see the full list of names, type
colors() into R.