We have described a new approach to colorimetric radiation sensing based on photonic polymer multilayers. Preferential degradation or crosslinking of the low-index polymer layers alters the degree of swelling of the irradiated region, thereby providing a colorimetric read-out of the exposed dose. While the sensitivity of these first generation devices is in the 100 kGy range, we anticipate that further refinements to the copolymers used should enable substantial improvements in sensitivity. Furthermore, the process allows for the preparation of robust multilayers on polymer substrates, offering the possibility to prepare flexible sensors.