Gladeshard vs Yellow Green

How close are they?

ΔE 23.9, loose: different enough that you should pick on purpose. Yellow Green is noticeably lighter, more saturated, warmer than Gladeshard.

Can I use Yellow Green instead of Gladeshard?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Yellow Green is noticeably lighter, more saturated, warmer than Gladeshard.

Can I use Gladeshard instead of Yellow Green?

The same difference applies the other way round: Gladeshard is noticeably darker, more muted, 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.