Well, I would say that the from the best that I can gather there are a few subs that are more collectible. The early ones like the 6202 surely come to mind. The 6536-1 which is the first of the straight edge case style, slim with no crown guards is fairly rare. It has a 1030 movement. The 5508 which is the same watch with a 1500 series movement is not as collectible but is still very desirable. People would likely say the 1530 is a better movement and so the 5508 is an easier watch to maintain but it doesn't seem to have the rareity or bring the money that the 6536-1 does, likely because it was made for a lot longer period of time and there are just more of them. The 6538 which is the Chronometer version with the BIG CROWN is more valuable and then there is the later version of that, the 5510. These are MUCH more expensive...thousands more. I am also trying to discern these subtleties and price differences as I become more an more enamored by the early versions. The dials I think were black but they have a clear laquer over them which yellows and makes it look brown but I could be wrong. My 5508 is like coffee ground brown...very cool with Gold writers and silver depth rating...absolutely a coool look. The brown is not wrong don't worry. I just don't know if they came that way or yellowed. That is really all I know. Good luck. Check out this site for nice info...I can't get the pictures to load but maybe you can.