Icy Grey vs Light Blue RLM78

How close are they?

ΔE 8.7, close: similar, with a visible difference side by side. Light Blue RLM78 is a little darker, more saturated than Icy Grey.

Can I use Light Blue RLM78 instead of Icy Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Light Blue RLM78 is a little darker, more saturated than Icy Grey.

Can I use Icy Grey instead of Light Blue RLM78?

The same difference applies the other way round: Icy Grey is a little lighter, more muted.

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.