Pokémon Diamond and Pearl, Cities/Routes...

[GrooveMan.exe]

I know that, but for me it never seems to save.. When I open the Rom again it's back to the start...

Augg, whatever, I will try again another time.

You need to change your battery save medium. You go to the Emulation Options and mess around with the settings.

But yeah OP, There'll be different colourations for Night, Morning, Day, and Evening. You might as well put the colouring differences on the same sheet (so Route 201 has all the times of day for that route, etc.)