The variation and inheritance of juvenile shell color and pigmentation pattern in the freshwater mussel, Hyriopsis cumingii, were reported in 1-yr-old progeny of eight families. There were three distinctive phenotypes of shell color and pigmentation patterns observed, including a greenish-brown shell with radial rays, yellowish-brown shell with radial rays, and yellowish-brown shell without radial rays. There were no greenish-brown individuals without radial rays. The shell color phenotypes showed variation with the growth in juvenile Stage I (1–3 cm in shell length), and the percentage of individuals with radial rays increased once they reached a shell length of 11 mm and then stabilized after reaching 20 mm in shell length. Shell color differentiation became more apparent at a shell length of 26 mm. Results of chi-square tests of the segregation ratio of shell color or ray phenotypes obtained from eight families at juvenile Stage II (6–9 cm in shell length) suggested that greenish-brown is controlled by a dominant allele (G) and yellowish-brown-shell phenotype is by a recessive allele (y); the ray pattern phenotype is controlled by a recessive (r) and a dominant allele (R) at a single locus. Shell color phenotypes may be a useful genetic marker for future selective breeding of triangle pearl mussels.