If you cross GG x gg, all of the offspring will be heterozygous, Gg. So 0% will be homozygous recessive and 0% will be homozgyous dominant.
If you use a Punnett square on this problem, it should be set up like this:
You can see that filling it out will yield four boxes all containing Gg. So there would be no homozygous recessive offspring (gg) and no homozygous dominant offspring (GG), because all of the offspring would be heterozygous (Gg). This also means that all of the offspring will be green, because the G allele is dominant and it confers green coloration.