This is a rare Rolex Submariner 5513 Tropical Dial No-Date that just sold at Antiquorum's May 13, 2012 auction in Geneva. The estimate was ($10,000 to $14,000) and not surprisingly, it sold for more than the high-end of the estimated value at $14,600. Tropical dial Rolexes - whether it is a GMT, Explorer or Submariner - command a significant premium over the same Rolex with a black dial.
Tropical dials likely came from a manufacturing flaw which caused the dials to turn brown after production. Factors such as sunlight, temperature and other environmental factors may have effected the dial color (especially when you consider the variances between different dials). However, it is widely believed that what caused the original paint material to change brown, was improperly formulated paint. Needless to say, tropical dial Rolexes are rare, and highly sought after by collectors.