In Gregor Mendel's study with the color or peas, which ones were dominant and which ones were recessive?

The peas with the purple flowers were dominant and the peas with the white flowers were recessive.  

Explanation:

In Gregor Mendel's study, he studied pea plants with purple flowers and white flowers.  The purple flowers were dominant, and whenever the allele for a purple flower was present is was visible on the plant.  The white flowers were recessive because if an allele for a purple flower was present, then the flower was purple.  The flowers were only white if both alleles were for white flowers.