Shamrock Green vs Olive Yellow

How close are they?

ΔE 38.1, loose: different enough that you should pick on purpose. Olive Yellow is a little lighter, more muted, warmer than Shamrock Green.

Can I use Olive Yellow instead of Shamrock Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 38). Olive Yellow is a little lighter, more muted, warmer than Shamrock Green.

Can I use Shamrock Green instead of Olive Yellow?

The same difference applies the other way round: Shamrock Green is a little darker, more saturated, 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.