Mostly a 1959 Les Paul called “Greeny”
Representative Les Paul — photo by Lightburst, CC BY-SA 4.0, via Wikimedia Commons
Peter Green's signature guitar was “Greeny,” a 1959 Gibson Les Paul Standard with a reversed, out-of-phase neck pickup. He played it through the Bluesbreakers and Fleetwood Mac before selling it to Gary Moore; it is now owned by Kirk Hammett.
For his classic recordings, Peter Green played “Greeny” — a 1959 Gibson Les Paul Standard whose reversed neck-pickup magnet gave it the unmistakable out-of-phase tone behind “Albatross” and “Oh Well.” That modification is now known as the Peter Green mod.
He was far from a one-guitar man, though: by his death he owned more than 150 instruments — Gretsch, National, Fender and more — sold at auction by Bonhams in 2023. But it's the ’59 Les Paul, later owned by Gary Moore and then Kirk Hammett, that defines the Peter Green sound.
Sources: Greeny (guitar), Wikipedia · GuitarPlayer