Warcry Green vs Green Sky

How close are they?

ΔE 21.4, loose: different enough that you should pick on purpose. Green Sky is noticeably lighter, more muted than Warcry Green.

Can I use Green Sky instead of Warcry Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Green Sky is noticeably lighter, more muted than Warcry Green.

Can I use Warcry Green instead of Green Sky?

The same difference applies the other way round: Warcry Green is noticeably darker, 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.