Middle Stone vs Light Mustard Khaki

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Light Mustard Khaki is cooler than Middle Stone.

Can I use Light Mustard Khaki instead of Middle Stone?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Light Mustard Khaki is cooler than Middle Stone.

Can I use Middle Stone instead of Light Mustard Khaki?

The same difference applies the other way round: Middle Stone is warmer.

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.