ΔE 21.5, loose: different enough that you should pick on purpose. Pearl Blue is a little lighter, much more muted, cooler than Elven Armour. They are different kinds of paint: Army Painter Elven Armour is a metallic and Tamiya Pearl Blue is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Pearl Blue is a little lighter, much more muted, cooler than Elven Armour. They are different kinds of paint.
The same difference applies the other way round: Elven Armour is a little darker, much more saturated, warmer.
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 Elven Armour on the colour wheel See Pearl Blue on the colour wheel
All matches: Elven Armour equivalents · Pearl Blue equivalents