Read the book 'til page 67 (if you haven't already). When the three characters (Ginger, Nat, and Pat Wald) realize that they're lost, the main character/narrator (Ginger) starts getting sap stuck to her hand (They don't mention which one.). First, she gets yellow sap from a stick that Nat hands her after they find a clearing but not the clearing where their parents were setting up camp. Later on, Ginger prevents Nat from climbing a tree by pulling him down. As she does, her hand rubs against red moss on the tree and gets red sap on her hand. Later, after losing Pat and having a close encounter with the big blue beasts (Fleg, Gleeb, Spork, and others with not-mentioned names) and learning that they're playing a deadly game, Ginger grabs a umbrella plant leaf to steady herself. The leaf shreds in her hand and drips blue sap on her hand. Then, when Nat figures out that the beasts' game is like tag, he runs to go tag one of them and Ginger throws a rock at him (but it hits a tree instead), the rock gets orange sap on her hand. Ya got that? She got yellow sap first, then red, then blue, then....if you've already read the book, you get the idea. After Nat touches the Penalty Rock, Fleg notices the four colors of sap on Ginger's hand and describes them as "Nubloff Colors". Ginger stares at her hand and narrates/thinks, "Yellow sap from the stick. Blue from the leaf of the umbrella plant. Orange from the rock. Nubloff colors?" Did she forget a color?