I think namor is wearing the green trunks just to piss off Reed because namor banged Sue.
Namor: "I don't need no steeenking stretching powers to please a woman you brainy faggot. Imperious Rex! Wait, I'm Namor, yet saying Rex out loud makes me want to masturbate to SockSue right now. Illuminati meeting paused. I'll be right back."