[R] plotting many line segments in different colors

[rif]

I want to plot a large number of line segments, with a color
associated with each line segment (I'm actually plotting a function of
the edges of a 2d graph, and I want to use color to indicate the level
of the function.)  I originally thought I could use lines, but lines
puts all its lines in one color (from help(lines), "col: color to use.
This can be vector of length greater than one, but only the first
value will be used.").

Is there a function that does what I want?  Right now I'm using the
obvious solution of calling lines in a loop with a single segment, but
this is really quite slow for my purposes, as I have several thousand
lines total to plot.

Cheers,

rif