Quick Silver vs Dark Gunmetal

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Dark Gunmetal is a little darker than Quick Silver.

Can I use Dark Gunmetal instead of Quick Silver?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Dark Gunmetal is a little darker than Quick Silver.

Can I use Quick Silver instead of Dark Gunmetal?

The same difference applies the other way round: Quick Silver is a little lighter.

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.