Pharaoh Guard vs Boreal Green

How close are they?

ΔE 17.7, loose: different enough that you should pick on purpose. Boreal Green is a little darker, more muted, cooler than Pharaoh Guard.

Can I use Boreal Green instead of Pharaoh Guard?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Boreal Green is a little darker, more muted, cooler than Pharaoh Guard.

Can I use Pharaoh Guard instead of Boreal Green?

The same difference applies the other way round: Pharaoh Guard is a little lighter, more saturated, 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.