LitCharts assigns a color and icon to each theme in Tuck Everlasting, which you can use to track the themes throughout the work.
The Purpose of Living
Childhood, Independence, and Maturity
Nature and the Cycle of Life
Morality, Choices, and Friendship
Summary
Analysis
A while later, the man in the yellow suit ties the Tucks' horse to the Fosters' fence and lets himself into the yard. He knocks on the door and notices that the lights are all still on. Granny opens the door and the man in the yellow suit cheerfully asks to come in: he knows where Winnie is.
Though the man in the yellow suit appears to be helping here, his appearances throughout the novel--and the fact that he stole the horse--tell the reader that he's not someone to be trusted and he's likely not choosing to act in Winnie's best interests.