I mean the green does definitely still seem in use, and given Sylvanas ranger armor, seems blue is Ranger General colors. But even now Liadrin is depicted with red armor in artwork -heartstone- with her latest appearance in game -Arathi and the rest of BfA- also wearing a red paladin armor.
It's not nothing that is rangers still use blues and green tho, as they have been several times pointed as the most traditionalists among the Blood Elves- but even so, it's markedly evident that as a whole, blood elves heavily have shifted to autumnal palettes, specially in military uniforms/gear.
Again, every race has aesthetics preferences, not exclusivity.
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I mean, San'layn are literally just another type of undead. San'layn customization IS undead customization, that the current undead skin + red eyes works for both allows more player choice.
Undead (Including San'layn) customization for BE's would have been an easy thing to add even as a "Night Warrior" equivalent, bummer that we didn't get it, but it doesn't close the door on San'layn as an AR (or whatever future equivalent of AR) so there's that.