Karak Stone vs Blackert Brown

How close are they?

ΔE 16.9, loose: different enough that you should pick on purpose. Blackert Brown is a little darker, more muted, warmer than Karak Stone.

Can I use Blackert Brown instead of Karak Stone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Blackert Brown is a little darker, more muted, warmer than Karak Stone.

Can I use Karak Stone instead of Blackert Brown?

The same difference applies the other way round: Karak Stone is a little lighter, more saturated, cooler.

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.