This is very tricky because the tiles have to fit into and follow irregular shapes, but RC is based on regular grids that may not play well with this style. To do the job properly I feel it might need some kind of packing algorithm. That said I've attached a sample file with a few approaches that may be helpful, be aware though that all these have the limitation of a fixed grid.
The first idea uses a purely RailClone approach, with an L1S generator used to define the outside edge and an A2S generate set to clipping mode to fill in between as shown below.
As you can see though the infill does not rotate to follow the direction of the boundaries. However if this is important it is something we can do with Forest Pack. Using Forest's new Effects
feature I can write a little script that rotate the tiles to face towards the nearest include area.
The script used for this is a adaptation of the the Look at Boundary with Falloff
effect that ship with Forest Pack 5, To change the colours in this example I have added a surface with different Material IDs, one for colour and then added the spline 6 times. Each time the area is added it adds a different coloured item by using Forest's Select Models by Area
and Limit to Surface Material ID
The issue with this technique is that you loose the nicely define boundaries that we saw in RailClone, so the 3rd example combines both plugins. RailClone is used to create the borders and Forest Pack fills in the area and allows the tiles to rotate to follow the boundaries.
To pull the Forest objects away from the edges a little to make space for the RC object you can use the Density Falloff feature that's found in the areas rollout. A stepped graph will give you a hard finish instead of a gradual fading out of tiles.
I hope that helps, if I can think of another approach I'll update this post but please let me know if you have any further questions.