You can explicitly set the 'CData' of a line object. This is what I did when I created a class for an RGB 3d line, this allows you to explicitly set the colour at each point which you can read from a colourmap if you wish or code via some other programmatic method.
In my case I wanted a line to run from a start point to an end point in RGB space which I would then colour appropriately, but since this was just a straight line I could define just choose an arbitrary number of points to define along it (I chose 100) and assign to each the appropriate colour. So my case was a little simpler
e.g. I define a line to go from [0.1 0.3 0.4] to [0.9 0.8 0.7] and it will use those coordinates both to position the line in 3d and to determine its colour end points and use a linspace between those two end points to give me my 100 colours to assign to the points.
