作中国地图时的颜色调整

R代码如下，用的是五普的各省出生婴儿性别比的数据，但无论如何也调整不好颜色，根本区分不出来，哪位高人指点一下？

library(maptools)
axx<-readShapePoly("bou2_4p.shp", proj4string=CRS("+proj=longlat +ellps=clrk66"))
x=axx
#plot(x,col=gray(924:0/924));#using col instead of fg!

getColor=function(mapdata,provname,provcol,othercol)
{
f=function(x,y) ifelse(x %in% y,which(y==x),0);
colIndex=sapply(mapdata$NAME,f,provname);
col=c(othercol,provcol)[colIndex+1];
return(col);
}

provname=c("北京市","天津市","河北省","山西省","内蒙古自治区",
  "辽宁省","吉林省","黑龙江省","上海市","江苏省",
  "浙江省","安徽省","福建省","江西省","山东省",
  "河南省","湖北省","湖南省","广东省",
  "广西壮族自治区","海南省","重庆市","四川省","贵州省",
  "云南省","西藏自治区","陕西省","甘肃省","青海省",
  "宁夏回族自治区","新疆维吾尔自治区");
pop=c(110.56,112.51,113.43,112.52,108.45,112.83,111.23,109.71,110.64,116.51,
  113.86,127.85,117.93,114.74,112.17,118.46,128.18,126.16,130.30,
  125.55,135.64,115.13,116.01,107.03,108.71,102.73,122.10,114.82,
  110.35,108.79,106.12);
provcol=rgb(red=0.5,green=0.2,blue=0.3);
plot(x,col=getColor(x,provname,provcol,"white"),border = "green",xlab="",ylab="")

那是因为pop的数字相差太小了。一个办法是你可以都减去最小值
pop <- pop - min(pop)
然后再试试看。我的系统是英文的，所以中文的程序没法运行，测试不了。你先试试看，不行再说。