Fixing Colored Hair slots:

The issue was related to Material Slot Names, the material slot names are EXTREMELY important. They seem to follow a very loose naming convention in the office but the main thing to consider is that:

Whatever the main hair material is, it needs to be referred to as a _ColorMaster Any subsequent connected materials that share the same colour need to be referred to as a _ColorSlave

In addition to this, you need to add the appropriate slot ID to these suffixes.

So for the case of @fertexhid hair. He has multiple Hair materials for a whole bunch of different cal meshes, but they are all connected to ColorSlot 1.

So for material slot names, I randomly tested:

loosebangs_ColorMaster1 bottom_ColorSlave1 bottom_sides_ColorSlave1 top_ColorSlave1 topsides_ColorSlave1 loosesides_ColorSlave1

and that worked.

Additionally, you cannot have any material slot share the same material slot name, so having two things called bottom_ColorSlave1 will confuse the colouring system they have setup and the game will default to colouring only one of the materials (which will most likely be the first known index)