Primer Taupe vs Satin Varnish

How close are they?

ΔE 37.3, loose: different enough that you should pick on purpose. Satin Varnish is noticeably lighter, more muted than Primer Taupe.

Can I use Satin Varnish instead of Primer Taupe?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 37). Satin Varnish is noticeably lighter, more muted than Primer Taupe.

Can I use Primer Taupe instead of Satin Varnish?

The same difference applies the other way round: Primer Taupe is noticeably darker, more saturated.

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.