There's a tradition in software programming for a developer to hide secret messages inside an application, known as Easter Eggs. There are several Easter Eggs in BusyCal.
Normally, BusyCal displays today's date with a blue background.
Holiday Easter Eggs
On certain holidays, BusyCal reveals its Easter Eggs by changing the Today color to match the holiday. Here are some examples for Independence Day (July 4th), Halloween (October 31st), and Christmas (December 25th).
According to the ancient Mayans the world will come to an end on December 21, 2012. We couldn't let that date go by without an Easter Egg. After all, it may be our last!
BusyCal displays a black and yellow striped banner on that date, warning you to get your affairs in order for the after life.
If the Mayans were wrong, and we live to see another day, on December 22nd the Today color will return to blue... until the next Easter Egg.