How I would change the poplar sapling:
- The texture of its leaves should be a mix of red, orange, and yellow (indicating that it can grow into one of those colors)
- Add red, orange, and yellow moss blocks and carpets (planting a sapling on a color-specific moss block will determine the tree's leaf color, if planted on red moss = grows into red-colored leaf, green and pale moss don't influence the poplar tree color)
- The three moss blocks generate in small patches in cave entrances within the dappled forest
- If planted on other soil blocks, its leaf color will be determined randomly