What would be the outcome of these crosses between pea plants, where the allele for purple flowers (p) is dominant and the allele for white flowers (p) is recessive at a flower color locus?

Assuming P is purple, p is white. (So purple is dominant over white).

You didn't state the crosses so I will give you some:
1. PPxPP - all PP progeny (purple)
2. pp x pp - all pp progeny (white)
3. PP x pp - all Pp progeny (purple)
I'll put the rest in a picture, because the best way to look at these is via a Punnett Square.