S.C.C. No.1A Very Dark Brown vs Hardened Carapace

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Hardened Carapace is a little darker, more muted than S.C.C. No.1A Very Dark Brown.

Can I use Hardened Carapace instead of S.C.C. No.1A Very Dark Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Hardened Carapace is a little darker, more muted than S.C.C. No.1A Very Dark Brown.

Can I use S.C.C. No.1A Very Dark Brown instead of Hardened Carapace?

The same difference applies the other way round: S.C.C. No.1A Very Dark Brown is a little lighter, 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.