ΔE 5.8, very close: most people won’t see a difference side by side. Holy White is a little lighter than Light Grey. They are different kinds of paint: AMMO by Mig Light Grey is an ink, glaze or transparent paint and Army Painter Holy White is a one-coat contrast-style paint, so they won’t behave the same on the model even where the colour is close.
Yes, for most jobs. Very close match (ΔE 6). Holy White is a little lighter than Light Grey. They are different kinds of paint.
The same difference applies the other way round: Light Grey is a little darker.
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 Light Grey on the colour wheel See Holy White on the colour wheel
All matches: Light Grey equivalents · Holy White equivalents