Palidecido means 'pale' or 'grown pale'. It's a less common word than simply 'pálido' and carries a more dramatic, almost poetic weight, suggesting a profound emotional or physical reaction.
In the song, Frankie Ruiz uses it to express his intense emotional state, singing, "Estoy palidecido y un poco asustado de ti" (I am pale and a little scared of you). This word vividly conveys his fear and vulnerability in the face of his lover's betrayal and the raw intensity of his feelings.
Frankie Ruiz opens this one sounding wounded rather than angry. Yo no sé, por qué me engañas (I don't know why you cheat on me) sits over a slow salsa vamp, and he turns the blame straight back on himself: Quizás la culpa fue mía que no supe / Imponerme desde el principio (Maybe the blame was mine, that I didn't know how to assert myself from the start). Then comes the demand the song is named for. Desnúdate mujer (Get undressed, woman) is not seduction. He wants to see El arte que tu tienes / Cuando haces el amor (the art you have when you make love). That is the skill she has been practising on somebody else, and he admits Estoy palidecido / Y un poco asustado de ti (I've gone pale, and a little scared of you).
The second half is the unmasking. Con tu cara infantil representaste / Un papel de gran actriz (with your childlike face you played the role of a great actress) is the sharpest thing he says, and Ya te quité la máscara (I've already taken your mask off) lands like a verdict. What stops it turning cruel is how plainly he still wants her. By the outro he is down to Te busqué, te busqué y te encontré (I looked for you, I looked for you and I found you), still trembling, still asking.