Color By Orientation Direction component as seen in the Scene Inspector
The ColorByOrientationDirection component is used to make particles change color depending on their dot product of their orientation to a reference orientation. Dot product essentially means how close in terms of angle is one direction to another. The colors when in-between are lerped.
The color to use if the particle's orientation is exactly 90 degrees to ReferenceDirection. This 90 degrees falls onto any particle direction that is along the surface of a plane facing the same direction as ReferenceDirection.