This activity engages students with the concept of mathematics identity to expand conceptions of what mathematics is and therefore what doing mathematics and being mathematical can mean. By mathematics identity, we refer both to ways a learner sees themselves and participates in mathematics, and the ways that others speak about or treat that learner in relation to the discipline of mathematics (Langer-Osuna, 2017; Martin, 2012). Specifically, the possibility of a learner being seen as mathematical, or expressing a mathematical identity, may be less a reflection of the individual learner's interests or abilities and more a reflection of "what" and "whom" those in positions of power - teachers, administrators, curriculum writers, assessment designers, policy makers, mathematicians, media representations, and so on - deem legitimately mathematical. The Math Identity Rainbows activity is meant to serve as an entry point for continued reflection and conversation around identity and power in the mathematics classroom, not an end point. When learners realize that their beliefs about their own mathematical competence have been shaped by the messages they have heard around competence, they can consider the possibility that their perceptions about themselves may be a result of their environments, rather than a fixed personal attribute.