Blue

Blue is Percy's favorite color, and is also a kind of running gag throughout the series. It's a sort of joke his mom and him play together from time to time.



History
Gabe once told Percy's mother, Sally, that there was no such thing as blue food. From that point on, she went out of her way to make blue foods to prove Gabe wrong. She would always bake blue cookies and buy blue candy for Percy. Also, Percy's favorite color is blue.

Percy Jackson and the Olympians
The Lightning Thief Sally always made blue food for Percy. When Percy came home from Yancy Academy, his mom brought some blue candies from the sweet shop she was working in, Sweet on America. To Percy, nectar tastes like his mom's homemade blue chocolate chip cookies. Also, when he first had dinner at Camp Half-Blood, he asked for his mom's "Blue Cherry Coke" to appear as his drink.

The Battle of the Labyrinth
At the end of the book, Percy's 15th birthday cake is blue.

The Last Olympian
Percy promises his mother that if he survives, he would give his mother some sort of sign, something blue. After Kronos is defeated, he asks Zeus to light up the top of The Empire State Building blue to let his mom know everything is okay. Without any argument, Zeus grants Percy's request. Later, Percy's birthday cupcake has blue frosting which, according to Percy, looks 'like a brick with extra blue cement' when Annabeth told him that Tyson helped her bake the cake.