2 different recipes. Brands sell different pigment mixtures under this name, so they won't all look or mix alike. Compare the pigments below.
Who makes it
PG18 Viridian + PY37 Cadmium Yellow1
- Holbein Artists' Oil Color No. H281
Sizes are the ones each line is sold in; marks a size only some colors come in. Check the store for a particular color.