In snapdragons, Mendel crossed red and white flowered plants. The red flowers on selfing produced only white flowers. He used 'R' to designate red flowers and 'r' for white flowered plants. When he crossed he obtained a pink coloured flower that showed an intermediate expression. On selfing, the $F_1$ hybrid, he got 1 red coloured flower, 1 white coloured flower along with 2 pink coloured flowers. Thus RR represented red flowers, rr the white flowers and Rr the pink colours respectively. In this cross red was not dominant completely and this exemplifies the concept of Incomplete Dominance.