ΔE 16.0, loose: different enough that you should pick on purpose. Monastic Green is a little darker, more saturated, warmer than Turnbull Turquoise.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Monastic Green is a little darker, more saturated, warmer than Turnbull Turquoise.
The same difference applies the other way round: Turnbull Turquoise is a little lighter, more muted, 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.
See Turnbull Turquoise on the colour wheel See Monastic Green on the colour wheel
All matches: Turnbull Turquoise equivalents · Monastic Green equivalents