[OT] two question about color space.
if you don't mind about the efficiency of your program, just use ? sapply on a range of wavelengths. I'm not particularly keen on the implementation of the FORTRAN program you used compared to the one I suggested, it seems like a very crude convolution.
Thank you very much for your suggestion, I will try to use ``sapply''. As for the Fortran program, it's not as accuracy as the C program you recommended, because it converts wavelength to RGB approximately.
The easiest way I know of is using ggplot2, see the last example of this page: http://had.co.nz/ggplot2/geom_path.html In base graphics, you could use segments to join the observations and supply a vector of colours of appropriate length.
Thanks again for your suggestion, I will try. Best regards, Jinsong