[Therion] Best approach for colouring elevations

[Tarquin Wilton-Jones]

Fun fact;
You don't even have to select the map for map lookups to find the scraps
inside it.

mycave.th:
survey mycave
  map foo
    myscrap
  endmap
  map bar
    myscrap
  endmap
  ...
endsurvey

thconfig:
source "mycave.th"
select bar at mycave
lookup map
  foo at mycave [100 0 0]
endlookup
layout elevation265
  color map-fg map
endlayout
export map -proj plan -layout local -o "mycave.pdf"

myscrap will be red, because it is in foo, even though bar is selected.
Needless to say, this is a little unpredictable (is it a feature or a
bug?), and means things get coloured even when you didn't expect them to be.