Based on the title provided, you are referring to the manga officially localized in English as (The Japanese title Shiro Buta Kizoku desu ga... translates to "I am a White Pig Noble, but...").
He didn’t smile. But he leaned against her shoulder, just slightly, and didn’t pull away. Hanako’s heart, merged with Violette’s, swelled until it felt like it might crack her ribs. Based on the title provided, you are referring
“It’s yellow,” he whispered.