With the revisit of class fantasy with narrowing down on hero specs I would like to suggest Death knight players be able to change their eye color from the standard blue. Yes, it is iconic and reminescent of the Lich King but in terms of spec flavor I think would be better for players to be able to choose and the blue color is kind of frost specific.
Similar to the Forsaken who received an eye color customization a couple years ago I think all death knight players should receive red if they want to emphasize blood or green to show the unholy. Also maybe purple if they want to have a more deathy look like the color of the old death rune.