Not the deadly arsenic variety!
In masstone a punchy, acidic green. Once white is added it just soaks it up due to the strong Phthalo pigment, the very acidic nature of Phthalo is offset by the gentler warmness of the Arylide.
All in all a strong green which will work well with other powerful hues. Slightly darker in tonal value than the swatch opposite suggests.
"A blend of organic lake colours (Arylide Yellow and Phthalo Green) with the two whites to give a safe and permanent substitute for the original Emarald Green, the notorious Copper Aceto-Arsenite, a brilliant green introduced circa 1810 and long since abandoned as being impermanent, highly reactive with other pigments and highly poisonous. My blend has none of these disadvantages. Some artists detest this uniquely strident colour, others love it acerbic tang, which invites an almost Fauve series of related mixes."
Pigment - PY3, PG7, PW6 & PW4
Opacity - Opaque
Vehicle - Linseed Oil
Tint Power - High