Sorry to burst the bubble: found this online at the Florida Museum of Natural History website (FLMNH Ichthyology Department: What Color Apparel or Gear Should I Wear in the Water To Help Avoid A Shark Attack
What Color Apparel or Gear Should I Wear in the Water?
Sharks see contrast particularly well, so any high contrast color apparel or gear used by a human in the water is especially visible to sharks. The bright yellow color traditionally used in water safety flotation devices and rafts is readily seen by human rescuers looking for missing persons in the sea and likely is seen easily by sharks as well. As a result, shark researchers laughingly refer to this color as "yum yum yellow!" Should one replace all these devices with more drab colored items? Of course there is a trade-off involved, but most would agree that the benefit of increasing one's chances of being rescued far outweigh the minimal risk of attracting a shark. By contrast (pardon the pun), divers and swimmers probably can reduce the chance of an interaction with a shark by avoiding bright swimwear or dive gear. I personally prefer to use dark blue or black fins, mask, tank, and wetsuit while diving and make a point of wearing my dive watch under the cuff of my wetsuit, thereby eliminating any chance of light reflection off the face of the watch attracting a shark or barracuda. Similarly, one always should avoid wearing jewelry because the glint of light reflecting off metal approximates the glint of light off the scales of fishes, the normal food items of most sharks.
© George H. Burgess, International Shark Attack File
Florida Museum of Natural History, University of Florida
I would get the yellow as a preference, and put the Rolex in a pocket.