Hishi mochi is a lozenge mochi (rice cake) which is prepare for girl 's day.
March 3rd is girl's day in Japan.
We call it "hina matsuri".
It is an event to celebrate in hope of the growth of girl in healthy.
Hishi mochi is formed three layers.
The third layer( green ) is kusa-mochi which is a rice cake flavored with mugwort.
Those three colours, pink, white and green , are compared to peach blossom, remaining snow and young grass( fresh leaf) each.