I’ve read somewhere that Rebel Without a Cause was actually shot in color, not black and white, but couldn’t believe it since the colors in it wasn’t too real! So was what I saw (colors) is real straight from the camera or it was just colorized years after the film?
Rebel Without a Cause was filmed in color. Interestingly, they started shooting it in black and white, but then switched to color because Jack Warner (president of Warner Brothers studios) believed that James Dean was a rising star and merited a color movie. They had to reshoot numerous scenes that were first filmed in black and white. Source.
If the color doesn't look real to you, it's probably because it was an early color film and the early color film didn't look as natural as later color film would.