To name a few:
Fresher material. Some constituents like anthrocyanin pigments darken as they age.
Early harvest. Clear trichomes produce a lighter extract than do amber trichomes.
Sativas typically lighter than Indicas
Higher ratio of Propane to Butane to limit longer chain molecules.
Sub zero extractions to limit longer chain molecules
Flood rather than soak.
Recover to high vacuum so as to produce cotton candy, which purges the raw oleoresin in bubble thin films.
Fast short final purge in vac oven in a thin film at <115F at -29.5" Hg, so as to not caramelize plant sugars