proper way of disconnecting PB from a monitor?

When you have the 'Book plugged into the monitor, are you using both screens, or is the PowerBook closed so you only have your one main screen?

If you are using it with the PowerBook closed, I would suggest opening it when you unplug the monitor, that way it will adjust back to the built-in screen, then close it to put it to sleep.

 

I run my PB in clamshell mode, which sounds like what you're doing. If you just unplug the monitor and everything from the PB, the PB won't go to sleep. Pressing the power button may have brought the PB display to life, and the blue screen is just the PB's view of the desktop. Generally, closing the lid, letting it really go to sleep, then waking it up works for me if I happen to mess up.

However, when I disconnect my monitor after being in clamshell mode, I open the PB first, disconnect all the cables, then close it so it falls asleep properly. Works every time.

If you're not running in clamshell mode, then you should be able to just unhook the monitor and go.