[Therion] Best approach for colouring elevations

[Tarquin Wilton-Jones]

> You have created two lookups for the same parameter (map), but no index has been specified.  i would guess that is why the last lookup overwrites.


Agreed. Ideally, it should warn me that I have overridden my lookup, and
that it is only using the last one. Right now, it silently tramples over
it, which is not a desirable response.