RLM 78 (1942) vs Light Feldgrau

How close are they?

ΔE 10.0, fair: the same colour family, but not a straight swap. Light Feldgrau is a little darker, more saturated, warmer than RLM 78 (1942).

Can I use Light Feldgrau instead of RLM 78 (1942)?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Light Feldgrau is a little darker, more saturated, warmer than RLM 78 (1942).

Can I use RLM 78 (1942) instead of Light Feldgrau?

The same difference applies the other way round: RLM 78 (1942) is a little lighter, more muted, cooler.

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.