That's true. Madara could simply be changing his appearance to keep his identity hidden, and fool his opponents, who are all around him.
This is Madara sixteen years ago, when he unleashed the Nine-Tailed Fox on Konoha and fought the Fourth Hokage, Minato Namikaze.
You must be registered for see images
Seven years later, Madara meets Itachi, who gives him the offer of eliminating the Uchiha clan, in exchange for promising not to attack Konoha.
You must be registered for see images
This is the present, where Madara walks with Kabuto after being approached and forced into an alliance, because of an unseen person's presence inside an Edo Tensei coffin summoned by Kabuto.
You must be registered for see images
Clearly great periods of time have passed since all these events, which would give Madara more than enough time to change his appearance as he wishes. Or, as Honord Sage says, he could be using genjutsu to feign a certain appearance, either so his true identity isn't discovered (if he indeed is not Madara), or simply to confuse the Kages and the ones he interacts with. After all, it confounds everyone on this forum, but everyone likes the mystery - it gives them more room to theorize, speculate, and just guess if they please.