ΔE 26.1, loose: different enough that you should pick on purpose. Nuln Oil is a little darker, much more muted than Dark Blue Tone.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Nuln Oil is a little darker, much more muted than Dark Blue Tone.
The same difference applies the other way round: Dark Blue Tone is a little lighter, much more saturated.
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 Dark Blue Tone on the colour wheel See Nuln Oil on the colour wheel
All matches: Dark Blue Tone equivalents · Nuln Oil equivalents