graphPolygonWithGradient: Plot a polygon with colour fill over a polygon with black...
In kendonB/bellmisc: What the package does (short line)

Plot a polygon with colour fill over a polygon with black lines.

graphPolygonWithGradient(colourVar, dataPoly, legendTitle, fileName, plotTitle,
  directoryPlots = getwd(), backPolygon = NULL, brewerPalette = "RdYlGn",
  fontFam = NULL, myrev = TRUE, limits = NULL, heightAdj = 1,
  widthAdj = 1)

`colourVar`	numeric variable that defines the gradient colour. Same length and order as dataPoly.
`dataPoly`	SpatialPolygonsDataFrame to be plotted.
`legendTitle`	legend title as character.
`fileName`	filename (not with directory or extension) as character.
`directoryPlots`	directory to store plots
`backPolygon`	optional background polygon to be plotted on top of - fortified or raw (prefortifying will be faster if several maps are being generated).
`brewerPalette`	brewer palette name as character. Default is "Spectral".
`rev`	logical to indicate if Brewer colours should be reversed.