ΔE 9.9, close: similar, with a visible difference side by side. Typhon Ash is a little darker than RLM 78 (1942).
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Typhon Ash is a little darker than RLM 78 (1942).
The same difference applies the other way round: RLM 78 (1942) 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.
See RLM 78 (1942) on the colour wheel See Typhon Ash on the colour wheel
All matches: RLM 78 (1942) equivalents · Typhon Ash equivalents