Camouflage replaces all types.
Battle Effect: Alters the POKéMON's type depending on the location. ~ Serebii
When a Pokémon uses Camouflage, it changes into one type. It replaces both Psychic and Water. Therefore it is impossible to have a quadruple-typed Pokémon.
As for Forest's Curse and Camouflage, the typing depends on what was used first. If the order went Forest's Curse > Camouflage, then Camouflage would override the Grass typing and become monotype. If the order was Camouflage > Forest's Curse, then the Grass type would be added to Camouflage's type, making the Pokémon dual-type. I hope that this is of use to you!