This was a series; I seem to remember reading it no later than the early/mid ’90s.
An important plot point was a set of non humans—blue, I think—that operated in a group mind to understand the ecology of a world. They could decide whether it was safe to colonize the world, and could assist a colony to set up on such a world to know exactly what was safe to eat, to do, where were good places to locate the colony, and so on. There was a fair amount of mysticism attached to it, and somehow a human woman became part of one of these group minds.
The bluemanoids weren’t inherently a group mind; normally, they were as much individuals as humans - but some of them had the talent to join into these ecology-aware group minds. When they were joined, only one of them could interact with other people, as the “voice” of the group mind.