we have described a model chemical system, which by virtue of the imposed microgeometry autonomously detects a macromolecular phase transition occurring in a thin film, and reports it in a visual form of color patterns. We suggest that micronetwork RD systems similar to the one described here might be useful in rapid assessment of absorptivities of other materials – likely, using different indicator/ink pairs and possibly with different solvents12. Finally, we believe that this work will stimulate new theoretical research on RD processes coupled by mass transfer and occurring in complex microgeometries.