Without A Shadow Of A Doubt, You're My Daisy
Leo said his favorite flower was daisies with a rather sad smile on his face the second time they met. Daisy now knew that daisies were Veronica's favorite flower. That would explain his reaction in some ways but not others.
She tried to remember what else he had said that day. After a moment, she recalled he said something about how her name suited her because he always thought of daisies as cheerful, friendly flowers. And how widely he had grinned at her when she embarrassed herself by complimenting his hair though the sadness lingered in his eyes.
Veronica talked about how pretty his hair was throughout the story. It would also explain why Leo said he had a rather sentimental reason for loving the color red even though it wasn't his favorite.