About one in 5-8% of men (estimates vary) suffer from some form of colorblindness. In its most common form, red and green are indistinguishable. Best practice is to avoid dependency on color for coding, popout, and highlights. Color should be combined with contrast, shapes, symbols, text labels and other approaches that will remain distinguishable for colorblind users.
As an added benefit, following this guideline will strengthen the desired effect of the color use for normal users and will remain effective on grayscale displays and printouts.
The Society for Technical Communication Usability SIG (Special Interest Group) has an excellent collection of resources on usability and colorblindness: http://www.stcsig.org/usability/topics/colorblind.html