Why not? They let night elf DKs change their eyes to the Night Warrior customization, so why can’t we let belves/velves/nelves have spooky red eyes as Death Knights?
You can choose the skin tone but the eyes remain blue and misty.
Yes, but… Night Warrior eyes broke that precedent, and established that it’s possible for other options to be there, but that they just don’t want to do it.
(Other note: There are apparently a bunch of unique demon hunter eyes tied to skin choice options but you can’t see them because of the blindfolds or felfire. Some people get around this with particular helmets that hide the blindfold.)
Also here’s a fun fact regarding that eye effect: It exists in black and white with a palette option applied to it. It isn’t a blue texture, itself. It makes it feel like they planned DK eye colors but just kinda went, “Eh, never mind.”
Because the Dark Ranger skin tones and eye colors are coupled together and someone was too lazy to take a few minutes to separate them. They were also too lazy to properly modify the Dark Ranger skins for player use, which is why the one for female blood elves and void elves causes the freckles on face option 3 to disappear.
Prior to SL, your character’s eye color was tied to what face you chose, but night elves only had one eye color by default and the Night Warrior skin options overrode it. The options weren’t class-restricted, meaning DKs and DHs could use them, so when SL overhauled the barber system and made Night Warrior eyes and skins separate from each other, the ability for DKs to have Night Warrior eyes was grandfathered in because Blizzard didn’t want to upset anyone by removing it entirely.
Actually, DKs and DHs can’t use Dark Ranger skin tones at all. If I go to character creation and look at, say, a male blood elf’s skin tones, then option 15 on a DK or DH (one of the tones exclusive to those classes) is different from option 15 on any other class (the Dark Ranger tone). Option 15 on a DK is similar to Dark Rangers, but not quite the same.