ΔE 16.6, loose: different enough that you should pick on purpose. Green Sky is a little lighter, much more muted than Resedagrün (RAL 6011).
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Green Sky is a little lighter, much more muted than Resedagrün (RAL 6011).
The same difference applies the other way round: Resedagrün (RAL 6011) is a little darker, much more saturated.
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 Resedagrün (RAL 6011) on the colour wheel See Green Sky on the colour wheel
All matches: Resedagrün (RAL 6011) equivalents · Green Sky equivalents