ΔE 20.8, loose: different enough that you should pick on purpose. Green Sky is noticeably lighter, warmer than Green Hell.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Green Sky is noticeably lighter, warmer than Green Hell.
The same difference applies the other way round: Green Hell is noticeably darker, 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 Green Hell on the colour wheel See Green Sky on the colour wheel
All matches: Green Hell equivalents · Green Sky equivalents