Staying in the black when glidiing

Spending 10 hours a day in my Prius taxi's I have plenty of time to work on my fuel saving techniques. Doing ok so far with most days ending up anywhere from 4.3 to 4.6L/100km fuel consumption. Considering that in my business that time is money and I can't be taking my sweet time getting to my destinations, I am happy with 4.3 to 4.6 but am always looking to improve.
I understand that being in the black is best and I get in the black but seem to have a hard time staying there for more than 20 seconds at a time unless I am on a downgrade.
My question is do you ever get to the point that you stay in the black for long distances without it switching to green or brown, or do you constantly have to adjust the pedal to get back to the black like I seem to have to do.
Most of my travel is between 40kmh and 80kmh throughout the day.
Our calls are computer dispatched so between having to constantly monitor the MDC computer and then watching the Prius monitor and also watching the traffic I have a lot of distractions as it is and would like to get better at staying in the black so that it isn't such a struggle to do so.