ΔE 10.6, fair: the same colour family, but not a straight swap. Light Feldgrau is a little darker, warmer than Hellblau RLM 78.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Light Feldgrau is a little darker, warmer than Hellblau RLM 78.
The same difference applies the other way round: Hellblau RLM 78 is a little lighter, 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.
See Hellblau RLM 78 on the colour wheel See Light Feldgrau on the colour wheel
All matches: Hellblau RLM 78 equivalents · Light Feldgrau equivalents