ΔE 17.8, loose: different enough that you should pick on purpose. RLM 78 Light Blue is a little darker, much more muted, cooler than Toxic Mist.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). RLM 78 Light Blue is a little darker, much more muted, cooler than Toxic Mist.
The same difference applies the other way round: Toxic Mist is a little lighter, much more saturated, warmer.
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 Toxic Mist on the colour wheel See RLM 78 Light Blue on the colour wheel
All matches: Toxic Mist equivalents · RLM 78 Light Blue equivalents