I hosted a "Purple Cow" party for my 3 year old daughter and her friends.  The invitations had the poem : "Have you ever seen a purple cow, I never hope to see one, but I can tell you anyhow I'd rather see than be one." printed on a velum overlay over purple cardstock. After the guests arrived, my daughter's great grandmother recited the poem and displayed for the kids a ceramic purple cow (attached with the story of how she received such a gift). The children were then to"spy" paper purple cows hidden throughout our backyard. As they found them they received little gifts of boxed candy etc... The kids were then served "purple cows" in plastic purple Sunday glasses with colored straws. These were given as favors after the party. The recipe for purple cows consists of pouring grape soda over vanilla ice cream.  Of course all paper products were purple. As an added treat, I had a puppeteer perform a small puppet show for entertainment.