What does Percy wish for as he puts his dinner into the fire in chapter 7 of Percy Jackson and The Olympians: The Lighting Thief By Rick Riordan

Percy thinks of his mother....

I said, “Cherry Coke.”
The glass filled with sparkling caramel liquid.
Then I had an idea. “Blue Cherry Coke.”
The soda turned a violent shade of cobalt.
I took a cautious sip. Perfect.
I drank a toast to my mother.
She’s not gone, I told myself. Not permanently, anyway. She’s in the Underworld. And if that’s a real place, then someday…