Small patches of very smooth plains material occur in the floors of many of the youngest craters. The patches may consist of fallback and impact melt related to the formation of individual craters and therefore may not represent late- stage volcanic fill or volcanic modification of the more youthful mercurian craters. Schultz suggested compositional differences or endogenic modification as possible causes of the color contrasts among the floor, wall, and rim areas of the dark-halo craters Zeami (129 km diameter), Tyagaraja (97 km diameter), and Balzac (67 km diameter). The dark ejecta and floors plains of these craters are distinctly redder than the surrounding plains, whereas their anomalously bright floor patches, central peaks, and wall areas are distinctly bluer. None of these dark- halo craters has associated bright rays, although secondary craters are well preserved. Compositional implications of contrasting color differences for mercurian crater and plains materials have been discussed by Hapke and others. The bright, bluish areas in these craters are now known to be hollows.Blewett, D. T., Ernst, C. M., Murchie, S. L., and Vilas, F., 2018. Mercury's Hollows. In Mercury: The View After MESSENGER edited by Sean C. Solomon, Larry R. Nittler, and Brian J. Anderson. Cambridge Planetary Science. Chapter 12.
