May I ask which model of Sylvanas are you referring to?
The details of the armor was actually based on Sylvanas' Action Figure and I believe it is purple as seen in this picture : [link] The cosplay as a whole was based on her current in-game model in World of Warcraft. Her hair there is dirty blonde.
But, I do agree with the skin. I'll have to mix some paint to get the exact color of Sylvanas which is grayish-blue.
You are right I took another look at the in-game model and her is a dirty blonde and her armor is purple, so my mistake. Other than the skin color great cosplay! I would recommend going with a light grey or silver for it rather than a mix.