Tombstone Yellow vs Light Mustard Khaki

How close are they?

ΔE 7.4, close: similar, with a visible difference side by side. Light Mustard Khaki is more saturated than Tombstone Yellow.

Can I use Light Mustard Khaki instead of Tombstone Yellow?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Light Mustard Khaki is more saturated than Tombstone Yellow.

Can I use Tombstone Yellow instead of Light Mustard Khaki?

The same difference applies the other way round: Tombstone Yellow is 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.