Karak Stone vs Flak Gun Yellow

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Flak Gun Yellow is a little lighter, more saturated than Karak Stone.

Can I use Flak Gun Yellow instead of Karak Stone?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Flak Gun Yellow is a little lighter, more saturated than Karak Stone.

Can I use Karak Stone instead of Flak Gun Yellow?

The same difference applies the other way round: Karak Stone is a little darker, 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.