Joe Jonas, Zayn Malik -- Hair-Off Continues ... But Joe Wins This Round

Joe Jonas and Zayn Malik continue to copy each other when it comes to their locks ... and this time, Joe's on top.

Both are now rocking pink tips, we're told Joe went for the look about a week ago and Zayn was spotted with a fan a couple days ago sporting the same doo. The two have been trading hairstyles for a while now.

As for Joe, we're told he thinks the whole thing's actually kinda funny.

Might we suggest some green next?