Speech-based interfaces that feature conversational agents have a diverse population of users, including children. While recent HCI research has investigated child-agent interactions in the context of speech-based interfaces with rare mention of sample populations' racial makeup, scant research has examined how racially minoritized groups, in particular Black youth, interact with such technologies. Subsequently, issues of race and racism continue to be largely neglected within the HCI community, contributing to technology that marginalizes Black people. Leveraging Black feminist epistemology as a critical framework, we engage Black students in the ideation process of conversational agents as speech-based interfaces, drawing attention to how race, gender, and class influence their design choices. Our findings reveal that Black students prefer custom-designed conversational agents that are modeled after Black women, possessing knowledge of Black culture and serving as life coaches to help them achieve their goals. We also confirm that the current design of speech-based interfaces perpetuates racism, reinforcing whiteness as the norm.CCS Concepts: • Human-centered computing → Collaborative and social computing.