Note that the yellow form seems to be a bit rarer among Verdant Dreamsabers, and you may need to kill a bunch before some spawn in this colour. The ones that turn into Pollenfused Dream Creatures cannot appear in yellow.
Level scaling: Most NPCs will scale with the Hunter's level, within the constraints of their level range. Hunters can tame regular NPCs up to 2 levels higher than them, but can only tame elite NPCs of the hunter's level or below.