How to change the color of a GL line?

I've searched but can't find an answer that works. None of the solutions that come up work for me. Here's my code:

 if (points.Count > 1) {
                 lineMat.SetPass (0);
                 GL.Begin (GL.LINES);
                 for (int i = 0; i < points.Count - 1; i++) {    
                     GL.Vertex3 (points [i].x, points [i].y, points [i].z);
                     GL.Vertex3 (points [i + 1].x, points [i + 1].y, points [i + 1].z);
                 }
                 GL.End ();    
             }

I've tried using GL.Color and changing the material color with lineMat.SetColor but neither solution works.

Changing the material with lineMat.color works, but I want to have different sections of the line be different colors (like a gradient), and changing the material color will change the entire line.