Ok , so I have seen a new loading screen talking about red diamonds which I had not seen before dawnguard.

Are they in the game now and has anybody found one?

don't remembering hearing about them before either, this is what the Wiki has to say......

http://elderscrolls.wikia.com/wiki/War_of_the_Red_Diamond

A paragraph in that wiki is pretty much what the loading screen says but I've not seen it before today and I have not come across a red diamond yet.

I havent seen any but ive seen but loads of regular and flawless diamonds.

I'm thinking it might be a quest item.