Firstly, I did an overall color palette change for the entire character. The original colors were way too vibrant for her to be a death knight, so I shifted everything to be a bit colder/bluer, such as skin tone, and shadows, as well as her eye color and gem color. Secondly, I started playing with more color variation, particularly in her hair. This is something I've been wanting to push and to play with more, so I'll be using this effect on the rest of the character once I have the overall appearance down.
You can check out the progression of this character here