[Therion] color centerlines by map?

[Jonathan Prouty]

I'm wondering how to make it so that each individual map will have a
uniquely colored centerline? This would be very helpful for differentiating
between different surveys at a glance. In the following example, I would
like to to have  clay_splay and clay_center be drawn in different colors.
The map that I am selecting in thconfig is clay_main, by the way.

<code>
  map clay_splay -proj plan
    splay.trip2
    splay.trip3
  endmap

  map clay_center -proj plan
    center.trip2
    center.trip3
  endmap

  map clay_main
    clay_splay
    clay_center
  endmap clay_main
</code>

I've attached a PDF that shows roughly what I have in mind, although the
alternating blue and green is not necessary. They can both be the same
color, as long as that color isn't the same as the centerline :-). Does
there happen to be a metapost wizard out there who might have an idea?
Thanks in advance!

-- 
-Jonny ^v^
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