Varying Grand Staff Color

Your problem is that you actually only have one grand staff and four systems. You can only change a staff to one color, so go into instruments and add 3 more instruments and adjust the number of measure and you can set each one's using right click and staff properties. You will need to do this on each staff.

It is not possible to do what you want on a single staff.
If you have four separate instruments, you can do it. (with 4 grand staff)
But you have to do it in the last stage. So after you finish writing. (For notes and rests)

And if you've add the instruments and changed the note line color further: select barlines or bar numbers, then right click->select->select similars in the same stave and change the color.

For a seperate key signature press "ctrl" and select it and change the color.

Enter the notes, select them right click->select->select similars in the same stave and change the color.

And last "hide empty staves".