Bi means someone may be attracted to blondes, brunettes, redheads, etc., but the ways in which they feel the attraction may be influenced by the hair colour. Pan means hair colour just doesn't play a role in their attraction. Neither inherently means that either is prejudiced against blondes who have dyed their hair, that they think purple isn't a valid hair colour, or that they don't recognize that hair colour exists in a spectrum.
(The generally accepted difference in the bi/pan community between bi and pan is that pan involves attraction regardless of gender whereas bi is simply attraction to 2 or more genders. Neither is inherently transphobic, although either can be, if the person is, because queerness is not a foolproof defense against transphobia.)
All that said, if you ask us, 90% of bi/pan folks will say that flag colours at least partially influenced which we choose to identify as.