He would need to cross one homzygous red (RR) and homzygous white (rr)
Explanation:
Flower color in snapdragons is controlled by a gene whose alleles exhibits incomplete dominance. The allele for red coloration (R) is incompletely dominant over the allele for white coloration (r). The intermediate phenotype that is produced in an heterozygous state (Rr) is PINK.
According to this question, a botanist wanted to produce a generation of snapdragons that all had pink flowers (Rr). This means that in order to do this, the botanist would need to cross a red snapdragon plant (RR) and a white snapdragon plant (rr) to produce an 100% Pink (Rr) snapdragon in the F1 generation.
