Pink Dates
I looked at this window for over a minute trying to work out which, if any, dates were pink. My girlfriend helped out by confirming that some were pink, but I still wasn't getting it. Then I happened to look at the screen from an oblique angle, and suddenly a few numbers looked different. It seems I was helped out by the relatively poor viewing angle on my PowerBook screen; the alignment of the sub-pixels leads to an occasionally helpful colour distortion.
We all need to pay attention to colour schemes, but maybe I should pay even more attention to usability for people with more serious disabilities than mere colour blindness.