The dominant pea seed color in Mendel’s experiments was yellow. In his crosses involving seed color, yellow seeds appeared as the dominant phenotype over green seeds.
Mendel studied seven pairs of contrasting characteristics in garden peas, including seed color, seed shape, flower color, plant height, pod shape, pod color, and flower position. For seed color, the two forms were yellow and green. When he crossed true-breeding plants with contrasting traits, the first-generation offspring showed the dominant trait.
When Mendel allowed the first-generation hybrids to self-fertilize, green seeds reappeared in the next generation. In a typical monohybrid cross, the visible seed-color ratio was about 3 yellow to 1 green. The underlying genetic ratio was 1:2:1: one homozygous yellow, two heterozygous yellow, and one homozygous green combination.
The question concerns seed color, not the color of the seed coat. Mendel’s list distinguished the yellow or green color of the seed and cotyledon from other features, such as seed texture, which could be round or wrinkled. Brown and white were not the standard contrasting seed-color pair in this experiment.