Shamrock Green vs Yellow Green

How close are they?

ΔE 18.7, loose: different enough that you should pick on purpose. Yellow Green is noticeably lighter, warmer than Shamrock Green.

Can I use Yellow Green instead of Shamrock Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Yellow Green is noticeably lighter, warmer than Shamrock Green.

Can I use Shamrock Green instead of Yellow Green?

The same difference applies the other way round: Shamrock Green 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.