Natural rubber instantly crystallises (reversibly!) under mechanical deformation. That is actually very desireable, because it gets tougher under load! High quality tyres (for trucks, not regular car tyres) today still contain quite a large amount of the world's natural rubber production for that reason.
You can try to pull at a lenght of the rubber tube, it should become pale, and go back to brownish-opaque when you release the pull.
The drawback is this also makes the material a bit brittle, if deformed beyond a certain limit. I believe this is what you see with your rubber tubing. If you unbend the kinks, the white colour should fade, but the tube is probably damaged at this point.