Administratum Grey vs Evil Flesh

How close are they?

ΔE 19.5, loose: different enough that you should pick on purpose. Evil Flesh is noticeably darker, more saturated than Administratum Grey.

Can I use Evil Flesh instead of Administratum Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Evil Flesh is noticeably darker, more saturated than Administratum Grey.

Can I use Administratum Grey instead of Evil Flesh?

The same difference applies the other way round: Administratum Grey is noticeably lighter, 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.