Blue diamonds are extremely rare, more rare than even pink diamonds. As with anything that is rare and well coveted its definitely going to be more expensive.
If this is true, it's only because white diamonds are more popular than black diamonds. The light bouncing inside the stone is more visible in the white and lighter colors. Given two diamonds, one...
Every diamond is valued by its cut, colour, clarity and carat weight. A local jeweler may be able to help you compare two similar diamonds, each with a different colour, and explain to you why one...