Hellblau RLM 78 vs A-28M Greyish Blue

How close are they?

ΔE 8.5, close: similar, with a visible difference side by side. A-28M Greyish Blue is more saturated, warmer than Hellblau RLM 78.

Can I use A-28M Greyish Blue instead of Hellblau RLM 78?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). A-28M Greyish Blue is more saturated, warmer than Hellblau RLM 78.

Can I use Hellblau RLM 78 instead of A-28M Greyish Blue?

The same difference applies the other way round: Hellblau RLM 78 is 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.