With my 3 and 5 colour Diamond hot ends, I always define the active and standby temperatures in the start gcode. There are probably other ways of doing it but this is something I set up a long a time ago and it fixed a lot of issues that I was having at that time so I've stuck with it.
So for example I'd have something like this (but this is for 4 tools):
G10 P0 S195 R195 ; Set tool 0 operating and standby temperatures
G10 P1 S195 R195 ; Set tool 1 operating and standby temperatures
G10 P2 S195 R195 ; Set tool 2 operating and standby temperatures
G10 P3 S195 R195 ; Set tool 3 operating and standby temperatures
Then at the end, I always turn them off by putting the following in the end gcode
G10 P0 S-273 R-273 ; Set tool 0 operating and standby temperatures
G10 P1 S-273 R-273 ; Set tool 1 operating and standby temperatures
G10 P2 S-273 R-273 ; Set tool 2 operating and standby temperatures
G10 P3 S-273 R-273
I use Slic3r rather than Cura. In earlier versions this meant having to use different printer settings for each filament as there was only one place to enter these gcodes. Later Prusa versions of Slic3r allow users to put custom gcodes in the "Filaments" section. It doesn't matter how it's done, as long as the commands get inserted before the print proper begins.
IMO it's generally best practice for any changes you make in the start gcode, to be reverted back to default settings in the end gcode. This will ensure that you don't carry over print specific settings to another print job.
HTH
