>>
Related to this can you tell me the purpose of the file globals.txt? Is it just to store the orginal
values of the global variables?
<<

globals.txt stores all the template globals and is the file used to generate the globals list in the admin panel. Everytime you add/remove a global it will be added/removed from globals.txt

>>
But it woud appear to be more involved than just changing the hex code
for the global variable 'dark green'.
<<

It shouldn't be. Any of the globals that are already a hex code by default can be changed to another hex code and it should update in the templates automatically. Did this not happen for you?