Currently, S. Korea is having some sort of crisis with her 10 won as the production of 10 won is said to be 36 won, thanks to the rising metal prices, which means the mint is making a total loss. To add to misery of both the mint and the field of numismatics, evil people have decided that melting down such coins are a lot cheaper than buying raw materials.
Sadly, this would probably mean that the currently 10 won design would not last too long and there are plans to make the coin smaller and out of cheap metal.
Ironically, this isn't the first time the Korean mint was forced to change the metal alloy. In 1970, the metal alloy in both 10 and 5 won were readjusted for cheaper cost. I cannot remember the percentage of the metals that were changed off my mind right now and I don't have my catalogue with me right now so allow me quote later.
Now this is an example of the previous 10 won:
And the modified 10 won:
There is actually no change in the design, diameter etc, except for the alloy content and hence explaining the color differences. I am not too sure what is rarer and that is what I will have to check later.
In the current Korean catalogue book that I have, they are differentiated by the color "red" and "gold" as seen from the picture. Perhaps if you are lucky, you might have both!
Perhaps... right now is the time to collect a type set of 10 wons before they are gone off to the metal refinery...
(Well I am trying at least 
)