ΔE 19.4, loose: different enough that you should pick on purpose. Eldar Robe is noticeably lighter, much more saturated than Night Lords Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Eldar Robe is noticeably lighter, much more saturated than Night Lords Blue.
The same difference applies the other way round: Night Lords Blue is noticeably darker, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Night Lords Blue on the colour wheel See Eldar Robe on the colour wheel
All matches: Night Lords Blue equivalents · Eldar Robe equivalents