One of my maps has 5 colors

Hi,
First off, thanks for the great work. This was just what I wanted.

Working with a map, I noticed that I got 5 colors. Is this a bug or some sort of freak occurrence.

My code:

library("rgdal")
library("raster")
library("MapColoring")

districts <- readRDS("IND_adm2.rds") #Downloaded from http://gadm.org  ->India, level 2
colors <- getColoring(districts)
cand.colors <- rainbow(20)
opt.colors <- getOptimalContrast(x=districts, col=cand.colors)
par(mar=c(0,0,0,0))

Printing out colors, I see that colors[265] and colors[270] for eg, have the value 5.
Cheers.

[bholtdwyer]

So does my map of U.S. counties.

[szhorvat]

This packages uses the DSatur colouring heuristic (or rather a variant of it), which, despite the claims made in the readme of "using a minimal number of colors", is not exact. DSatur does not guarantee a 4-colour solution for maps. So what you see is not surprising.