`Redcoat' soldier bean cultivar originated from off-type, virgarcus patterned seeds found in a foundation seed lot of `Red Hawk' dark red kidney bean (Phaseolus vulgaris L.). These off-type seeds were hypothesized to be the result of a single gene mutation. A mutation at either of two loci involved in bean seedcoat pattern expression, T or Z, could convert self-colored seedcoats to a virgarcus pattern. The results of test-crosses of `Redcoat' and `Red Hawk' to lines with known alleles at the seedcoat pattern loci indicate that the dominant T allele of `Red Hawk' mutated to recessive t in `Redcoat'. The mutant t gene prevents expression of red veins in wing petals due to v rkd, and enables expression of the z gene (and possibly other genes) carried cryptically by `Red Hawk'. On the basis of preliminary data, we speculate that the two types of virgarcus patterns observed (classic in `Redcoat' and standard in the tester) may be controlled by different Bip alleles as they interact with t z.