Google Maps has very useful traffic data but it plots that traffic data using colors. For example, here is a screen capture of traffic new NYC:
But those that are severely colorblind are not able to see traffic data. One such person posted a complaint in Google Help Groups asking for an "alternative way" of displaying such data on Google Maps for those that are colorblind.
Interesting point, making Google Maps more accessible for the colorblind.
Forum discussion at Google Help Groups.
Update: In August 2009, Google has taken steps to help the colorblind see traffic on Google Maps.