How this plays out depends on the particular theory under consideration. If we look at Hume's position, then what you are discussing is merely personal preference and has nothing to do with morals. In other words, Hume would agree with you that trying to apply morals to that particular question is silly.
(For Hume, morality has to do with sentiments or feelings of benevolence or the feeling of humanity. Other feelings are not the source of morality, and are non-moral. Thus, the preference for chocolate versus vanilla is not a moral issue, since that preference has nothing to do with feelings of benevolence.)