color.scale calculates a sequence of colors by a linear
transformation of the numeric values supplied into the ranges
for red, green and blue. If only one number is supplied for a
color range, that color remains constant for all values of x.
If more than two values are supplied, the x values will be
split into equal ranges (one less than the number of colors) and
the transformation carried out on each range. Values for a color
range must be between 0 and 1.
If extremes is not NA, the ranges will be calculated from
its values using col2rgb, even if ranges are also supplied.
extremes allows the user to just pass the extreme color values
in any format that col2rgb will accept.
If the user wants to specify a range of values with xrange,
it must at least include the range of x values. This can be useful
when there is a notional range like 0-100 cover, or when several series of values with different ranges are
to be assigned the same color scale.
The user may not want the color scheme to be continuous across some
critical point, often zero. In this case, color scale can be called
separately for the values below and above zero. See the second example
for color2D.matplot.
# go from green through yellow to red with no blue x<-rnorm(20)
y<-rnorm(20)
# use y for the color scale plot(x,y,col=color.scale(y,c(0,1,1),c(1,1,0),0),main="Color scale plot",
pch=16,cex=2)