Cancer cells inside a single tumor are monoclonal; that is, they are family, all traceable back to a common ancestor. Within a tumor family tree, however, genetic instability produces branches that are wildly different from one other. How can scientists track these “families” inside a tumor and identify the most invasive and dangerous? One could label each family with a different colored fluorescent protein, but only a few protein colors are available and there are many families to track. So, like painters with a limited palette, researchers created varied mixtures of red, green, and blue proteins inside cells, revealing the rainbow of different families seen here.