You're right, they symbolize virtue.
Goodman's wife Faith (quite a symbolism in names, don't you agree?) is gentle and innocent, just like a wife should be in Puritan understanding. She doesn't really change in the story, nor does her character evolve - but Goodman's character does, as well as his relationship with his wife. To be perfectly clear, pink is an ambiguous color - just like Goodman's relationship with Faith. It is innocent (therefore, virtuous), but it is also a little bit frivolous and unstable - it is neither red, nor white.
