Matt White Primer vs Gloss Varnish

How close are they?

ΔE 7.3, close: similar, with a visible difference side by side. Gloss Varnish is a little darker than Matt White Primer.

Can I use Gloss Varnish instead of Matt White Primer?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Gloss Varnish is a little darker than Matt White Primer.

Can I use Matt White Primer instead of Gloss Varnish?

The same difference applies the other way round: Matt White Primer 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.