ΔE 3.8, very close: most people won’t see a difference side by side. Nuclear White is a little lighter than Matt White Primer. They are different kinds of paint: Army Painter Matt White Primer is a technical paint or medium and Green Stuff World Nuclear White is an opaque base/layer 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 4). Nuclear White is a little lighter than Matt White Primer. They are different kinds of paint.
The same difference applies the other way round: Matt White Primer 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 Matt White Primer on the colour wheel See Nuclear White on the colour wheel
All matches: Matt White Primer equivalents · Nuclear White equivalents