Administratum Grey vs Viridian Green

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Viridian Green is a little darker, much more saturated than Administratum Grey.

Can I use Viridian Green instead of Administratum Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Viridian Green is a little darker, much more saturated than Administratum Grey.

Can I use Administratum Grey instead of Viridian Green?

The same difference applies the other way round: Administratum Grey is a little lighter, much more muted.

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.