Rose gold is a blend of classic yellow gold with silver and copper added which will create the classic rose colour.
As with other types of gold, 18ct rose gold is softer than 9ct. This is because 9ct has less pure gold and a higher proportion of harder metals. The colour of rose gold is affected by the carat, 9ct being pinker in comparison to 18ct which appears more yellow.
Rose gold hallmarking is 375 for 9 carat rose gold with 37.5% being pure gold and 62.5% being the added alloys
Rose gold hallmarking for 18 carat rose gold is 750 which is 75% being pure gold and 25% being the added alloys