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