I'm not sure about the early costumes, but I do know quite a bit about the symbolism of red.
Red does often represent passion, yes. However, it can also represent courage (hoorah! we all know that theme
), rage, sacrifice, power, love, vitality, action, confidence, determination, impulse, adventure, ambition, assertiveness, health, life, and death (last three mainly because of its connection to blood). Red harbors a ton of energy, which is reflected in Pan's free, fun-loving spirit. Conversely, red also holds strong emotion, particularly the more impulsive kind, which are also reflected in his somewhat selfish, harsh self.
The color green - which is the color most seem to associate with Pan - actually doesn't appear to match his character quite as well as red. Green is often associated with healing, calm attitudes, renewal, generosity, prosperity, growth (! with Pan?), balance, and contentment...all attributes that don't speak of Pan's character.
I'm not sure at all if Barrie wished for Pan to be dressed in red, but the symbolism of the color alone reflects the character so well, it's hard not to wonder.