All of the offspring resulting from a cross between a red snapdragon and a white snapdragon are pink. what is the possible explanation for this?

It can be explained by incomplete dominance.

Explanation:

Incomplete dominance is a type of non-Mendelian inheritance.  When the phenotype of heterozygous is intermediate between the two homozygote phenotypes (according to Mendelian inheritance, heterozygous has the same phenotype as dominant homozygous).

In the example above, heterozygous genotype has pink phenotype which is between red (dominant homozygous) and white (recessive homozygous) phenotype.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).