Stone Grey vs Ivory Tusk

How close are they?

ΔE 8.5, close: similar, with a visible difference side by side. Ivory Tusk is a little lighter, more muted than Stone Grey.

Can I use Ivory Tusk instead of Stone Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ivory Tusk is a little lighter, more muted than Stone Grey.

Can I use Stone Grey instead of Ivory Tusk?

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