Smoke Grey vs Yeti White

How close are they?

ΔE 9.3, close: similar, with a visible difference side by side. Yeti White is a little lighter, more muted than Smoke Grey.

Can I use Yeti White instead of Smoke Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Yeti White is a little lighter, more muted than Smoke Grey.

Can I use Smoke Grey instead of Yeti White?

The same difference applies the other way round: Smoke 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.