What is mhw rainbow pigment?

Rainbow pigment is a special reward that hunters can unlock in Monster Hunter World (MHW). It is earned by completing all of the optional quests in the game, including the ones that require capturing specific creatures. The Rainbow pigment can be applied to your armor and weapons, and it will allow you to change the colors of your gear to almost any shade imaginable. This gives players the freedom to create their own unique look and stand out from other hunters. Additionally, the achievement of unlocking the Rainbow pigment demonstrates that the player has completed all of the challenges the game has to offer, and is truly a master hunter.