The color of Poplar leaves depend on what minerals are under sapling+dirt

• Poplar tree spawns with red leaves if sapling+dirt are on top of Cinnabar.
• Poplar tree spawns with yellow leaves if sapling+dirt are on top of Sulfur..
• Poplar tree spawns with orange leaves if sapling+dirt are on top of Block of Raw Copper.

Or

• Poplar tree spawns with red leaves if sapling+dirt are on top of Block of Raw Iron.
• Poplar tree spawns with yellow leaves if sapling+dirt are on top of Block of Raw Gold..
• Poplar tree spawns with orange leaves if sapling+dirt are on top of Block of Raw Copper.

Or

• Poplar tree spawns with red leaves if sapling+dirt are on top of Granite
• Poplar tree spawns with yellow leaves if sapling+dirt are on top of Diorite..
• Poplar tree spawns with orange leaves if sapling+dirt are on top of Andesite.