Morning Sky vs Light Blue RLM76

How close are they?

ΔE 19.8, loose: different enough that you should pick on purpose. Light Blue RLM76 is noticeably lighter, much more muted, warmer than Morning Sky.

Can I use Light Blue RLM76 instead of Morning Sky?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Light Blue RLM76 is noticeably lighter, much more muted, warmer than Morning Sky.

Can I use Morning Sky instead of Light Blue RLM76?

The same difference applies the other way round: Morning Sky is noticeably darker, much more saturated, 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.