Quote (checkout @ Aug 6 2017 11:54am)
Rainbow Goblins spawn in all areas of the game, including Nephalem Rifts where they may be part of larger Goblin packs. Like all Goblins, they will not appear in Greater Rifts, though.wiki is misleading, another source:
The only problem is that you are in a rift and portals to The Vault and Whimsydale don't spawn in rifts. This post was edited by Arcolithe on Aug 6 2017 01:55pm