Question

a particular plant is said to be homozygous for seed color. whatdoes this mean?

Answer 1

In other words the genes are the same for seed color so its going to be both upper case or both lower case. 
homo=same 

Answer 2

If you look at the prefix of homozygous, it "homo" which means the same. So if a particular plant is said to be homozygous for seed color, the alleles are the same.