ΔE 7.5, close: similar, with a visible difference side by side. Alizarin Green is a little darker than Niblet Green.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Alizarin Green is a little darker than Niblet Green.
The same difference applies the other way round: Niblet Green 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.
See Niblet Green on the colour wheel See Alizarin Green on the colour wheel
All matches: Niblet Green equivalents · Alizarin Green equivalents