Turquoise Ghost vs Monastic Green

How close are they?

ΔE 7.1, close: similar, with a visible difference side by side. Monastic Green is a little darker than Turquoise Ghost.

Can I use Monastic Green instead of Turquoise Ghost?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Monastic Green is a little darker than Turquoise Ghost.

Can I use Turquoise Ghost instead of Monastic Green?

The same difference applies the other way round: Turquoise Ghost is a little lighter.

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.