There is no certain ingredient formula for the so-called red gold/pink gold. One thing is for sure, however, that 75% of the alloy is AU (gold).
There is no SIGNIFICANT difference between red gold and pink gold. As you can see, there is no models with both red gold AND pink gold available simultaneously.
Following explanation was quoted from well-known .
Rose gold is a gold and copper alloy widely used for specialized jewelry due to its reddish color. IT IS ALSO KNOWN AS PINK GOLD AND RED GOLD.
Since it is an alloy, there is no such thing as "pure rose gold"; pure gold is yellow and pure copper is reddish.
Although the names are often used interchangeably, the difference between red, rose, and pink gold is the copper content: The higher the copper content, the stronger the red coloration.
source: http://en.wikipedia.org/