The purple colour of the flower is homozygous and dominant to white flowers in pea plant.
Explanation:
In Mendelian Genetics the dominant allele is always expressed masking the recessive allele in between dominant and recessive alleles.
It is present when two copies of the dominant gene are present.
Suppose a purple flower plant is crossed by white flower.
Purple flower PP and white flower is pp
P P
p Pp Pp
p Pp Pp
all the flowers formed are heterozygous and exhibit purple colour flower.
Thus we can see the purple colour is dominant and heterozygous.