For internal use.
choropleth.plot(sp, dem = "P0010001", cuts = list("quantile", seq(0, 1, 0.25)), color = list(fun = "hsv", attr = list(h = c(0.4, 0.5, 0.6, 0.7), s = 0.6, v = 0.6, alpha = 1)), main = NULL, sub = "Quantiles (equal frequency)", legend = list(pos = "bottomleft", title = "Population Count"),type=NULL, ...)
Zack W. Almquist (2010). US Census Spatial and Demographic Data in R: The UScensus2000 Suite of Packages. Journal of Statistical Software, 37(6), 1-31. http://www.jstatsoft.org/v37/i06/.