Shield Brown vs Green Yellow

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Green Yellow is a little lighter, cooler than Shield Brown.

Can I use Green Yellow instead of Shield Brown?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Green Yellow is a little lighter, cooler than Shield Brown.

Can I use Shield Brown instead of Green Yellow?

The same difference applies the other way round: Shield Brown is a little darker, warmer.

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.