ΔE 8.0, close: similar, with a visible difference side by side. Flanker Blue is a little lighter, more saturated, warmer than RLM 78 (1941).
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Flanker Blue is a little lighter, more saturated, warmer than RLM 78 (1941).
The same difference applies the other way round: RLM 78 (1941) is a little darker, 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.
See RLM 78 (1941) on the colour wheel See Flanker Blue on the colour wheel
All matches: RLM 78 (1941) equivalents · Flanker Blue equivalents