Tomorrow is Yellow Pig Day. It's been celebrated on July 17 since the 1960s. I'm surprised you haven't heard of it! Or, if you attended Princeton and/or majored in math, maybe you have.
Here's the background. Two math students, Michael Spivak and David C. Kelly, were given an assignment to analyze the properties of the number 17. They must have stayed up late, or taken chemical study aids, or something, because they went a little crazy and decided to invent an imaginary yellow pig that would have 17 toes, 17 teeth, 17 eyelashes, and so on.
How we moved from there to having it be a holiday is not answered in my sources (see below). This holiday is to be celebrated by eating Yellow Pig Cake and singing Yellow Pig Carols.
I have information that the 17th is also, coincidentally, Peach Ice Cream Day. I supposed Peach and Yellow aren't that far removed on the color chart, so you could celebrate them together. Put the Peach Ice Cream on the Yellow Pig Cake?
In case you decide to celebrate, here are some Yellow Pig Carols: http://www.yellowpigs.net/yellowpigs/YP_songs
If we can have a Yellow Pig Day, we should also have a White Pig Day. So I hereby declare today, July 16th, White Pig Day. I'm doing so, of course, in honor of Marshmallow, the pig featured on the cover of my second mystery, SMOKE.
pig pix are public domain from http://www.clker.com/